The type of offense that trespassing is in most places is simply a misdemeanor offense depending on where you trespassed.
If you trespass on federal property then the trespass charge could be a felony but if you trespass on someone's property then it may simply be a misdemeanor.
Most times when you get caught trespassing you'll get a trespass warning.
The trespass warning will then tell you that if you come back and trespass again that you'll go to jail for the trespass.
You can then bail out of jail but then have to show up in court and could face 6 months to a year in jail depending on your past criminal history.
Trespass can be charged as a felony, a misdemeanor, or an infraction depending on where you're trespassing and your criminal history and whether or not it was or is your first offense or it's happened more often.