Diving terms for your vacation: what brevet, check dive, and house reef mean

On a diving holiday, many words are used that no one uses at home. Here are the most important ones, sorted by the moment you encounter them, from booking to the wind that decides the dive site of the day.

Certificates and courses

Brevet

The brevet is your diving certificate. It shows what training you have and how deep you are allowed to dive. Show it with your logbook at the dive centre before the first dive, so it belongs in your carry-on luggage.

Open Water Diver

The beginner certificate. With it, you dive to 18 m in calm conditions, which is Level 1 in the guides. PADI and SSI follow the same standard, ISO 24801-2. What the course costs and how it works is explained in Diving certificate in Koh Tao.

Advanced Open Water Diver

The next certificate, often in two days with five dives. In the guides, it stands for Level 2, deep experience up to 30 m and currents. Many deep wrecks and pinnacles require it, for example, the Um El Faroud in Malta, the Chumphon Pinnacle before Koh Tao.

PADI, SSI, RAID and CMAS

These are training organisations. For you, the organisation counts for little. PADI states that it accepts certificates from other organisations for further training, and many dive centres accept divers with certificates from PADI, SSI, NAUI, RAID or CMAS for the next course.

Try diving

A day in the sea with an instructor, without a certificate. The organisations call it Discover Scuba Diving or Try Scuba. Many dive centres go no deeper than 12 m, in Thailand, a supervisor leads no more than two participants since April 2025.

Nitrox

A breathing gas with more oxygen than air. The dive centres only fill it if you show a Nitrox brevet. On Koh Tao, it costs an extra 200 to 400 baht, on some safari boats in the Red Sea, Nitrox is free up to 32 percent.

Before the dive

Medical questionnaire and certificate

Before the first dive, you fill out a questionnaire about your health at the dive centre. If you tick yes to certain questions, you need the certificate of a doctor who clears you. Therefore, read the form at home, see Checklist for the diving holiday.

Check dive

A first dive with a guide, where the dive centre sees how safely you dive, and you check your equipment. Many dive centres require it if your last dive was a long time ago. On Koh Tao, Crystal Dive wants to see a dive in the last six months, Big Blue a refresher in the last twelve. In Marsa Alam, you do it at the house reef, after that you go into the water there alone with your buddy.

Briefing

The discussion before the dive. The guide explains entry, route, depth, current and signals. No guidebook replaces the briefing, because only the dive centre knows the current, visibility and boat traffic of the day.

Logbook

Your proof of dives, on paper or in an app. The dive centres want to see it, for some sites the number of logged dives counts. For example, you may go to the Thistlegorm from 20.

Buddy

Your diving partner. You dive together, check each other's equipment beforehand and stay within visibility range underwater.

Level

This is how the guides of the atlas classify every site. Level 1 is suitable for Open Water up to 18 m and calm water, Level 2 for Advanced up to 30 m with possible currents, Level 3 for a deep diving or wreck special course and experience up to 40 m.

Underwater

Current dive and drift

During a current dive, you let the current carry you along the reef, and the boat picks you up at the end. Before Cozumel, you descend over sand for this, and the usually gentle current carries you to the reef wall. Because you can surface far from the entry point, dive centres there require a separate surface buoy.

Surface buoy

A buoy that you let surface at the end of the dive on a line, so that the boat sees you. A buoy with a reel belongs on every jacket with which you surface at the boat or in a current.

No-decompression limit

The time you can stay at a depth without having to make decompression stops on ascent. The deeper, the shorter. Your dive computer calculates it continuously.

Thermocline

A boundary in the water below which it suddenly gets colder. In Malta, the sea is 26 °C at the top in August, at 30 m only 18 to 21 °C. Which suit then fits is explained in Which wetsuit for which water temperature?.

Halocline

In the cenotes, fresh water lies above salt water. The boundary between them is called the halocline, and when you dive through it, visibility blurs for a few seconds.

Cavern and cave

The cavern is the part of a cave into which daylight still falls. In the cenotes, a guide on a line leads you there, for most Open Water is sufficient. Into the cave behind it you only go with the appropriate training. More in Cenote diving.

Overhead

This is the name for any place where there is a ceiling above you, so cave, breakthrough or the inside of a wreck. You cannot surface directly there. Into the inside of a wreck like the HTMS Sattakut before Koh Tao you only go with wreck training.

Places and types of diving

House reef

The reef directly in front of the hotel, camp or dive centre, which you reach from the beach or pier without a boat. In Marsa Alam, you usually dive at the house reef, at the Marsa Shagra camp from 6 to 20 o'clock. On Koh Tao, Calypso has a house reef in Tanote Bay, on Koh Phangan Haad Yao Divers.

Pinnacle

A rock peak that reaches from the bottom to just below the surface in open water. The Chumphon Pinnacle before Koh Tao starts at around 14 m, its foot is at 36 to 40 m. Schools of fish are attracted to pinnacles, and before Koh Tao whale sharks come there, see Whale sharks before Koh Tao.

Dive safari

A week or longer on a boat that goes from reef to reef and where you live. In the Red Sea, you can only reach the Brothers Islands, Daedalus and the reefs in the deep south this way. The shipping companies usually require 10 to 20 logged dives for this, for the Brothers 30 to 50 depending on the shipping company.

Hyperbaric chamber

In a hyperbaric chamber, doctors treat a diving accident under pressure. Where the nearest one is located belongs to the emergency plan, that is why the guides mention it for every destination. Check before the trip if your insurance pays for the treatment.

Wind and weather

Whether a site is doable is often decided by the wind. You hear these names at the dive centres.

Majjistral and Grigal

In Malta, the Majjistral blows from the northwest, on around one fifth of the days. Then the southeast side of the islands lies calm. Rarer, but cool and strong, comes the Grigal from the northeast, especially in winter.

Trade wind and Calima

In the Canary Islands, the trade wind usually blows from north to northeast, strongest in summer. The south coast of Lanzarote then lies in the wind shadow. Calima means air from the Sahara, which brings dust, most often from December to February.

Chamsin

A hot, dry desert wind with dust. In the Red Sea, it is possible from February to June.

Nortes

Cold fronts with wind from north to northwest, which pass through the Caribbean from October to March and bring waves to the west coast of Cozumel. Mostly they are over quickly.

Monsoon

In the Gulf of Thailand, the northeast monsoon brings the most rain from late October to early January. Then the dive centres on Koh Tao dive on the west side. From mid-May, the southwest monsoon blows, then the boats go to the east side.

Sargassum

Brown algae that float in carpets in the sea and are washed onto beaches. In the Caribbean, they come after the Cozumel band from April to October.

How you plan everything together is explained in Planning a diving holiday in six steps. The equipment from the mask to the wing is explained in My diving equipment, part by part. Every guide in the Atlas explains at the beginning how it shows level, current and entry.