Proto-language

A proto-language is the ancient language that all other languages came from. Imagine it like a kind of root language that all the other languages are branches off of. For example, English, Spanish and German are all related to each other because they share a common ancestor language. This ancestor is called the proto-language, and it is the earliest language known in history. By looking at the shared words and grammar of related languages, linguists can figure out what the proto-language must have sounded like.