Ahoy is a word used to signal a ship or boat, stemming from the Middle English cry, 'Hoy!'. The word had fallen into obsolescence before rising from obscurity as the sport of sailing rose in popularity. 'Ahoy' can be used as a greeting, a warning, or a farewell.

Ahoy is a combination of the call 'hoy' plus the sound 'a', presumably added to draw more attention to the cry. 'Hoy!' was a common call in England to drive cattle. The earliest known example is from William Langland, in whose 1393 epic poem, Piers the Ploughman, the word first appears in Middle English: 'And holpen to erie þis half acre with ’hoy! troly! lolly!'

'Hoi' is used in Modern Dutch as an informal greeting equivalent to English 'hi' or 'hey'.

Alexander Graham Bell originally suggested 'ahoy' be adopted as the standard greeting when answering a telephone, before 'Hello' (suggested by Thomas Edison) became common. In The Simpsons, Mr Burns is usually heard answering the phone with the greeting 'Ahoy-hoy'.

In Czech and Slovak, 'Ahoj' (pronounced [ˈaɦɔj]) is a commonly used informal greeting, comparable to "Hello". It was borrowed from English, and gained wide currency by the 1930s.

Greeting is an act of communication in which human beings (as well as other members of the animal kingdom) intentionally make their presence known to each other, to show attention to, and to suggest a type of relationship or social status between individuals or groups of people coming in contact with each other. While greeting customs are highly culture- and situation-specific and may change within a culture depending on social status and relationship, they exist in all known human cultures. Greetings can be expressed both audibly and physically, and often involve a combination of the two. This topic excludes military and ceremonial salutes but includes rituals other than gestures.

Greetings are often, but not always, used just prior to a conversation.

Some epochs and cultures have had very elaborate greeting rituals, e.g., greeting of a king.

Secret societies have clandestine greeting rituals that allow members to recognize common membership.

A greeting can consist of an exchange of formal expression, a simple kiss, a hand shake or a hug. The form of greeting is determined by social etiquette, as well as by the relationship of the people.