Chainline, which is the distance from bike centerline (seat tube centerline) to the center of the chainrings; If 3 rings, then to the middle ring. If 2 rings, to the midpoint between the 2 rings. The goal is for the chainline spec to line up with the middle of the stack of cogs on the cassette, this will give best overall shifting.

My 2X crank with 68mm BB shell has 43.5mm as chainline (has integral hollow spindle, no square tapers, so no length choice there), which works perfect with my 130mm dropouts and 7 speed cassette (road crank, road dropout spacing). I originally spaced the crank out 4mm due to an interference issue between the front derailleur lip and my very fat seat tube, and it shifted terrible, dropped the chain a lot. Remedied the derailleur issue and took out the spacers, shifted perfect, the way the bike gods intended.

If your new crank says in specs, same BB shell width, and same dropout width or says "road" or "mountain", should have the proper chainline with the BB spindle length it specifies.

Also, Q-factor is a choice, how far apart the pedals are; Usually a "road" crank is closer/lower q-factor, "mountain" crank is usually farther/higher q-factor, crank arms a bit more splayed outboard, better to clear fatter chainstay tubes.