Hindmilk refers to the fatty milk that is produced towards the end of a breastfeeding session. It is richer in fat and calories, which provides important nutrients and helps baby's growth and satisfaction.
There is a foremilk / hindmilk imbalance in your make because you either have a too fast letdown, you have an oversupply of milk, or you switch boobs far too often. (momwoot.com)
If they're kinda frothy and light greenish, though, baby might not be getting enough hindmilk because of an oversupply or because they're not being allowed to nurse long enough before switching breasts. (romper.com)