What does Boxing Day have to do with boxing?
Under control; in hand; together: got everything wrapped, whole fuckin' world on the half-shell (1980s+)
Code which is combined with another piece of code to determine how that code is executed. The wrapper acts as an interface between its caller and the wrapped code. This may be done for compatibility, e.g. if the wrapped code is in a different programming language or uses different calling conventions, or for security, e.g. to prevent the calling program from executing certain functions. The implication is that the wrapped code can only be accessed via the wrapper.