Meaning is metabolic.
From below, you are a system that converts energy into structure. Every meaningful act — feeding a child, laying a stone, finishing a thought — is the same fundamental transaction: a low-entropy output sustained against the second law. The body does not know the difference between a poem and a meal; it knows only whether the gradient was held or it was let slip. To live meaningfully, in this frame, is to keep the gradient — to keep building, against decay, the small structures that you alone can build. Death is when the gradient inverts. Meaning is everything you held against it.
Meaning is the felt sense of consistency.
From the middle, meaning is what arises when your actions, over a long horizon, line up with what you say you care about. It is not a feeling that comes during the act — it comes later, when you look back and see a shape. People who report 'meaningful' lives are usually not happier in the moment than people who report 'happy' lives; what they report is something quieter — a sense that their life is theirs, that they would not trade it. That sense is built, daily, by small alignments between attention and value. It cannot be bought, performed, or purchased in retrospect. It can only be deposited.
Meaning is what you would defend.
From above, the question reverses. Stop asking what is meaningful. Ask: what, if it were taken from me tomorrow, would feel like a wound? What, if I were never seen doing it, would I still do? What, if no one remembers it, am I willing to make? The answers are usually small and unglamorous — a person, a craft, a quiet promise to oneself. They look like nothing on a résumé. They are the entire ledger. Camus said one must imagine Sisyphus happy. The harder claim is older: one must imagine Sisyphus, mid-roll, choosing the rock.