Sour fruit is a term used to describe fruits that have a tart or acidic taste. Sloes, SLOE, LIME, LEMON, and crabapple are all examples of sour fruit. Sloes are small, dark blue fruits with a tart flavor, while SLOE is a type of plum with a similar taste. Limes are green citrus fruits with a sharp flavor, and lemons are yellow citrus fruits with a sour taste. Finally, crabapples are small, tart apples with a sour flavor.