Hi Nitesh!

Matter waves are the part of quantum mechanics, all the matter exhibit wave like behaviour, thus these waves are called matter waves. For example consider any water wave or a beam of electrons can be diffracted just like a beam of light . These are also called De- Broglie waves.

In- phase waves : If two waves have identical frequency and they cross the x - axis at same point and in same direction, then the waves are called in-phase.

Out of phase: If two waves have different frequency and they do not move in same direction, also they cross the x-axis at different points then these are called out of phase waves.

You can visit the link given below to learn more:

https://school.careers360.com/

Thankyou!