buttermilk

Short definition from Wiktionary

Noun

1. 1
   The liquid left over after producing butter from full cream milk by the churning process, also called traditional buttermilk.
2. 2
   Cultured buttermilk, a fermented dairy product produced from cow's milk, with a characteristically sour taste.
3. 3
   A light yellow color, like that of buttermilk.