Tap for spoiler
It’s a preposition. My Merriam-Webster Spanish-English dictionary has 15 definitions for it by itself: for (during), around (during), around (a place), by (through, along), for (for the sake of), because of (on account of), for (in exchange for, instead of), by means of, as for, times (as in multiplication), from (according to), as (for), by, and for (in order to).
When used with other words it goes up to 23 definitions like por favor meaning please.
Portmanteau of X (current name) and Twitter (former name)