In criminal law what do the charge entry without permission mean?

It means that you entered a building without breaking in. For example, if you walked through an open front door of a home without permission.

Added: Although this specific charge does not exist in the criminal statutes of many states, it falls somwhere between Trespassing and Burglary or Forcible Entry (i.e.: more serious than one, but not as serious as the other).

For example, entering someones house without permission is trespassing, but entering with intent to commit a crime therein is a burglary. (as per Florida Statute 810.02)