what has come forth from a source: the children and descendants a person has produced, or the growth a stretch of ground sends up
The word is built straight on the ordinary verb for going out or coming forth (יָצָא), and it means little more than "the things that have come out." Hebrew applies that to two sources without changing the word. A person's children have come out of him, and a field's growth has come up out of it, so one noun names both. Nothing in the word itself says which source is in view; the sentence around it does.
It is a rare word and a poetic one. All eleven of its appearances are in Job and Isaiah, it is always plural, and it usually sits in the second half of a poetic line answering the ordinary word for seed or offspring (זֶרַע) in the first half. Its job in those lines is to say the same thing a second time in fresher words, not to add new information. There is one small difference of picture worth noticing: the common word stays singular even when it means a whole nation, because it names one continuing line, while this word is plural and looks at descendants as many, spread out and countable.
Because it belongs to poetry, the word carries weight rather than detail, and it swings between promise and threat:
- descendants as thick as the grass of the field, standing in front of a man while he lives (Job 5:25, Job 21:8)
- descendants soaked with God's spirit and blessing, recognized among the nations as a people God has blessed (Isaiah 44:3, Isaiah 61:9)
- descendants who never get enough bread, and a field whose growth is torn up by the roots (Job 27:14, Job 31:8)
English versions therefore spread it across "offspring," "descendants," and "children" where a person is the source, and across "produce" or "what comes from it" where the ground is.