What is actually the difference between path tracing and ray tracing? Mostly they seem to be the same?
Ray tracing refers to the mechanical process of tracing a ray through a scene and figuring out what it hits. There are many applications of ray tracing. Ray traced reflections, ray traced shadows, ray traced AO etc.
Path tracing is also an application of ray tracing - but unlike those individual ‘effects’, path tracing addresses the whole of the rendering process in a single algorithm.
Specifically, in a path tracer, ray tracing is at least used to advance each path segment, and often for NEE (Next Event Estimation) light sampling visibility (shadow) tracing and similar. As an example, for a single pixel path traced sample, the path tracer might use anything from 5 to 50 or more ray traces depending on the properties of the encountered surfaces.