Hello Pratyush!

I shall try to answer this question without diagram.

Matter waves is a term that you come across in quantum theory of particles. they are also known as de-broglie's waves . Unlike electromagnetic waves, matter waves do not have electric and magnetic fields. They represent the probability of finding a particle in space . This concept evolved with idea that like waves can exhibit particle nature, particles too can exhibit wave nature.

Two waves are said to be in phase when the difference in their wave angles are 2n(pi) where n is a natural number.

Two waves are said to be out of phase when the difference in their wave angles or phase angle is 2n(pi) + 180 degrees.