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Correct answer: D. A full conversation that keeps running with no terminal attached, which you can open, reply to, and leave again
Explanation
The principle — the word to hold onto is conversation: a background session is one you are not currently sitting in.
Why the key is correct — Anthropic's definition carries all three properties at once: each background session is a full Claude Code conversation that keeps running without a terminal attached, so you can open it, reply, and leave whenever you want. And separately: background sessions don't need any terminal open to keep working, so closing the window you dispatched from changes nothing.
Why the others are wrong — a terminal is not what keeps it alive. It is not a subagent, which belongs to the conversation that spawned it. And it is not a fire-and-forget task, because you can rejoin it mid-flight.
Remember this — a background session is a conversation you can walk away from and walk back into.
Sources — Anthropic's documentation on managing multiple agents.
Sources
“Each background session is a full Claude Code conversation that keeps running without a terminal attached, so you can open it, reply, and leave whenever you want.”
“Background sessions don't need any terminal open to keep working.”
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