Wavefront at any instant is defined as the locus of the particles of the medium vibrating in the same phase. Every point on the wavefront acts as a source of the disturbance, these disturbances from the points are called wavelets. Each point on a wave surface can act as a new source of smaller spherical waves which are called wavelets. The wavelets may originate from the primary as well as a secondary source of light. Wavefronts are the envelope of these wavelets.