Che cosa significa Ostia ?

Vedi una traduzione

Depends on the context, but it's usually slang:

"¡Ostia!" - Just to express shock or anger (like the F word).

"Ser la ostia" - Used to express that you like something or someone a lot. Just be careful with this one, it can mean exactly the opposite (you'd be insulting someone) depending on how you say it and the context.
Example:
"Mi padre es la ostia" Can either mean: "My dad is so cool!" or "My dad is an a**hole" depending on the tone of my voice and my facial expression :D

"Dar/darse/pegar/pegarse una ostia" - Means to hit or be hit very hard. Sounds really harsh and rude.
Example: "Se dio una ostia con la bici" (He crashed his bicycle)
Example: "Como no te calles te doy una ostia" (I'll beat the s**t out of you if you don't shut up)

"A toda ostia" - Used to express that something is going fast. Also very slang.
Example: "El profesor habla a toda ostia y nunca me entero" (The teacher talks too f*cking fast and I never understand anything).

There are maybe more meanings, as usual with bad words in Spanish, but these are the ones that came to my mind now.

This was a lot of fun to explain :D