Pure plus 粋, which you might remember as "stylish" but which can mean pure as well. Wow, that's double the purity for this word. No wonder it also means pure!

純粋 is usually for pure-hearted people or feelings, like 純粋な心 (a pure heart) or 純粋な気持ち (pure feelings). You can also say 純粋な疑問 — for genuine doubt or innocent wondering that just popped into your head, purely out of curiosity, with no hidden motives.

This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.