Ahoj

1. Hello and Goodbye
Unlike English, ahoj works for both arriving and leaving. It functions similarly to the Italian ciao, but remember that ahoj is familiar in tone. Friends, family and children are common addressees; conventions can also make it normal among people who have not met before, such as in some recreational groups.

2. The Vocative Case
When you say ahoj followed by a name, use the vocative case for direct address. Some names have the same form in the nominative and vocative. For example, Petr becomes Petře (Ahoj, Petře!) and Jana becomes Jano (Ahoj, Jano!).

3. Saying 'See you...'
For farewells, you can sometimes attach ahoj directly to time expressions as a highly colloquial shorthand. For example, adding the particle tak to make tak ahoj zítra casually means 'see you tomorrow'. The standard way to say this is uvidíme se zítra or just tak zítra.

4. Addressing a Group
When greeting multiple people, it is very common to use the phrase ahoj všichni (hi everyone). In Moravia and Slovakia, you might also hear the pluralized form ahojte.

5. Addressing One Person or a Group
With one friend whom you address as ty, say Jak se máš? With several friends, use plural vy forms: Jak se máte? Formality depends on the relationship and local custom, so ahoj alone is not a grammatical rule requiring singular ty.

6. Written and Phone Communication
Ahoj is also the standard opening and sign-off for informal written communication, such as text messages and emails to friends or family. Additionally, it is the standard phone greeting when answering a call from a friend or family member, sometimes expressed as the warm No ahoj! (Oh, hi!).

7. Alternatives and Variations
A very common interchangeable alternative to ahoj is čau (derived from Italian ciao), which also works for both hello and goodbye. You will also frequently hear the affectionate diminutive ahojky, especially in text messages and casual speech among close friends.