A financial state in which someone's assets — investments, savings, or other income-generating property — produce enough income to cover their living expenses indefinitely, without requiring active employment.
It's the "FI" half of FIRE, and it's worth separating from the "RE" (retire early) part: plenty of financially independent people keep working, just because they want to, not because they have to. The core idea is about removing money as the reason you show up somewhere — what you do with that freedom afterward is entirely up to you.
Usually the same math as a FIRE number — comparing annual expenses to portfolio size and an assumed safe withdrawal rate. Once your assets can sustainably cover your spending, you're financially independent, whether or not you ever stop working.