A wash is watercolor paint diluted with water; more water the lighter the color will be.
Layers of watercolor washes on top of each other is called Glazing.
Each layer of paint should be dry before applying the next.
Work from light to dark and start with lots of water and little paint.
Music:
Fluidscape by Kevin MacLeod is licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/by/4.0/)
Source: http://incompetech.com/music/royalty-free/index.html?isrc=USUAN1100393