Ask HN: Why is the source folder called 'src'?

Many languages and frameworks advocate (or even enforce) a standard folder structure that includes a 'src' folder. I always found 'src' to be quite "ugly" and also possibly confusing to beginners, who might think it's an abbreviation of a multi-word phrase instead of a contraction. In the end, it only reduces the word by 3 letters. Why isn't it simply called 'source'? Does it have historic reasons? Or is it just laziness?