It is a measure of how your actions get you closer to your goals.

Hence, if my goal is learning Japanese, and I spend time in reading raw manga, I can argue I’m being productive. However, if my goal is to learn Rust, then reading raw manga is not being productive.

Productivity does not have an end goal other than what you set for yourself.

EDIT:

Edited the last sentence to make it say what I meant it to say. “Productivity has an end goal…” isn’t it. 😅