the.com/butter bean

means A large, pale, creamy-textured bean — the mature, starchy form of the lima bean, popular especially in Southern US and British cooking.

from 'Butter bean' is simply a descriptive nickname, earned by the bean's smooth, buttery texture and pale yellow-white color when cooked. It's the same plant as the lima bean (Phaseolus lunatus, named for Lima, Peru, where Europeans first encountered it), but regional naming split the two: in much of the American South and in Britain, 'butter bean' became the preferred term, especially for the larger, starchier varieties, while 'lima bean' stuck in other regions — leaving one bean living a double life under two names.