means The way a person is raised and cared for through childhood, including the values, manners, and habits instilled by parents or guardians.

from A plain English compound bolting "up" onto "bring" — the same "bring up" you still use when you say someone "was brought up well." English has a fondness for these up- creations (upkeep, upstart, upshot), and "upbringing" arrived as the noun for the long process of bringing a child up into adulthood. The "bring" itself is deeply old, traceable to Old English bringan, with cousins across the Germanic languages.