what is the difference between wide band and multiband antennas?

Wideband antenna provides a specified impedance match (i.e. <2:1 or < 3:1) over a continuous frequency band (i.e. an octave).

Multiband antenna is impedance matched to some level around harmonics or unrelated intervals.

Another answer you may be looking for is this. A wide band antenna provides continuous coverage across some band. A multiband antenna may not have continuous coverage. In fact, it may only offer a good impedance match over a narrow band of frequencies, but will provide a good match at several frequencies, with breaks in between.