What is the Difference between load bearing and frame structure?

Trusses and frames are both composed of triangular members connected at joints.

In a truss, the joints are pin type joints and the members are free to rotate about the pin. As such, a truss cannot transfer moments and members are subjected to only axial forces (tensile and compression).

On the other hand, members of frames are connected rigidly at joints by means of welding and bolting. Therefore the joints of frames can transfer moments in addition to the axial loads.

In a practical setting, you may see trusses with no flexibility in joints, but it is still acceptable to analyse them as a perfect truss.