There are no official or agreed upon definitions for superyacht or megayacht, but these terms are regularly used to describe large, luxurious, professionally crewed motor or sailing yacht, ranging from 40 metres (130 ft) to more than 180 metres (590 ft) in length and sometimes include yachts as small as 24 metres (79 ft).
The "Large Commercial Yacht Code (LY2)" of Great Britain and its dominions defines a "large yacht" as one that is 24 metres (79 ft) or more at the waterline and is in commercial use for sport or pleasure, while not carrying cargo or more than 12 passengers and carrying a professional crew. The code regulates the equipping of such vessels, both at sea and in port×including such matters as crew duty times and the presence of a helicopter on board. The code has different levels of standard for vessels above and below 500 gross tons. Other countries have standards similar to LY2. Whereas yachts of 24 metres and below may be constructed of fiberglass, larger yachts are more likely to be constructed of steel, aluminum or composite fiber-reinforced plastic. Such yachts may be considered "superyachts" and are more commonly at 40 metres (130 ft) or more in length.
Each superyacht has a flag state where it is registered, but may have never visited. Common flag state registrars for large yachts are Cayman Islands, Marshall Islands, Isle of Man, and the British Virgin Islands, among others.
Some yachts are used exclusively by their private owners, others are operated all year round as charter businesses, and a large number are privately owned but available for charter part-time. As of 2018, superyacht charter costs ranged between 70 and 550 thousand euros. Expenses of approximately 20–30%, such as food, fuel, and berthing are charged as an extra, called the advance provisioning allowance.
A 50-metre (160 ft) yacht may have one or more yacht tenders for reaching shore and other water toys which may include a speed boat or sailing boat, personal water craft, windsurfing and diving equipment and a banana boat. Such yachts have multiple screen displays and satellite communications.
Superyachts may be accompanied by a support (or shadow) vessel that carries such items as watercraft, helicopters or other large items that the yacht, itself, cannot readily accommodate. Such vessels range in length from 20 to 100 metres (66 to 328 ft). There are at least four manufacturers that specialize in building such vessels. One 67-metre (220 ft) example included the following amenities: a helicopter deck, six guest rooms, two-story helicopter hangar with sound system, movie theater, freshwater pool, a landing craft, four each of: jet skis, kayaks, sailboats, diving and fishing gear, and water skis. For use ashore, there were reportedly a two-seater automobile, two motor scooters and two bicycles. The vessel also featured a 35-tonne (35,000 kg) crane.
All superyachts have crew areas below deck, which consist of a crew mess, crew cabins and laundry. While most crew cabins contain bunk beds, there are captains and chief engineers who, on the larger yachts, have their own cabins. There are no set hours that crew members work each week. The hours depend greatly on how often the owners are on board, how often it is chartered and on what hours the captain sets when there are no guests on board. The crew can be hired through crew agencies or various websites.