If you’re wondering about the term itself, wiktionary has some background:

Not known with certainty. Two long-held hypotheses are as follows: One describes combat soldiers wistfully wishing to go back home, buy a farm, and live peacefully there; later, after they had been killed in combat, their fellow soldiers would say that they had bought the farm (compare the established metaphor pattern of having gone to that big [whatever sort of nice place] in the sky). Another links the phrase to the idea that governments compensate farmers whose land is damaged by a military aircraft crash; a deceased pilot was thus said to have bought the farm, and the term eventually entered wider use.

(idiomatic, US, informal, euphemistic) To die; generally, to die in battle or in a plane crash.

This idiom is most often found in its past tense and past participle form bought the farm.