I am enchanting my boots [minecraft Xbox 360] but I always get projectile protection. But I don't know what it means?
Directly from the minecraft wiki, as there's not really anything more to add than a basic definition.
Includes damage from arrows, ghast/blaze fire charges, etc.
As you might expect, "Projectile protection" does in fact, protect you from projectiles...
It's worth noting that this will NOT protect you if a Ghast projectile explodes near you (That would require "Blast Protection")
In case this is a problem of translation, here's Google's definition of "Projectile":
An object propelled through the air, especially one thrown as a weapon.