What does “Muttersprache” mean in German?

Muttersprache is your native language, the one you grew up in, built plainly from Mutter (“mother”) and Sprache (“language”). The handy part is the pattern: German labels every kind of language by bolting a describing word onto -sprache. Learn Muttersprache and you’ve basically learned a small family of words that all work the same transparent way.

Alongside it sit Zweitsprache (second language, used daily), Fremdsprache (a foreign language you study), and Amtssprache (official language) — the clip even glosses that last one as die offizielle Sprache. A native speaker is a Muttersprachler (or Muttersprachlerin), swapping -sprache for the -sprachler person-ending. Same building blocks, rearranged.