It's a bit of a circular definition, but it's because the word "Malayalam" is the name of the language. It's like saying the English meaning of "English" is "English."
However, the word itself is believed to have originated from a combination of two words:
* "Mala" (meaning "mountain" or "hill")
* "Aalam" (meaning "country" or "region")
This suggests that the language was initially spoken in the hilly regions of Kerala, which is where the name "Malayalam" is associated with.