What is the "Marketing review" tab next to my message history?

It holds marketing that needs a human decision — chiefly one customer matched by several campaigns at once — with Approve all / Discard all or one at a time. The same tab carries your weekly per-customer cap; set it to 0 and every marketing WhatsApp waits for your approval. Approved messages go out on the next run, 10:00–21:00 your time.