Define Huygens' principle?

Question

Complete defination please

Answer 1

1.Each point on a propagating wave can be considered as the source of a small wave, or wavelet which propagates at the same speed as the original wave. The new wave front for the propagating wave can be constructed by drawing a line tangent to the edges of these wavelets.
physics.neiu.edu/reference/glossary.html

2.Every point on any wave front can be regarded as a new point source of secondary waves.
www.nksd.net/schools/nkhs/staff/john_daneau/cp_glossary.htm

3.Huygens principle (named for Dutch physicist Christiaan Huygens) is a method of analysis applied to problems of wave propagation. It recognizes that each point of an advancing wave front is in fact the center of a fresh disturbance and the source of a new train of waves; and that the advancing wave as a whole may be regarded as the sum of all the secondary waves arising from points in the medium already traversed. ...
en.wikipedia.org/wiki/Huygens'_principle

Answer 2

'' all points on a given wave front are taken as point sources for the production of spherical secondary waves, called wavelets, which propagate outward through medium with speeds characteristic of waves in that medium. After some time interval has passed, the new position of the wave front is the surface tangent to the face wavelets. '' Physics for Scientists and Engineers 6e by Serway and Jewett, Page 1107

Answer 3

It recognizes that each point of an advancing wave front is in fact the center of a fresh disturbance and the source of a new train of waves;helps in explaining phenomenon like diffraction(i.e. bending of light at sharp obstacles)

Answer 4

huygen's principle states that every point on a wavefront acts as a source of fresh disturbance referred to as secondary waveletts.