Sour is a basic taste that is acidic, sharp, and often unpleasant, like the taste of a lemon or vinegar.
The word "sour" can also describe:
1. Milk that has gone bad - "The milk has turned sour."
2. A person's mood or attitude - "He gave me a sour look."
3. A relationship that has become unpleasant - "Their friendship turned sour after the argument."
4. In music, a sour note is one that is off-key or unpleasant to hear.