means A pod is a small protective casing that holds seeds (as on a pea or bean plant), or by extension any compact, self-contained unit — a sleeping pod, an escape pod, a group of whales.

from From Middle English, and likely a back-formation from "podware" or "podder," old words for seed-crops and the husks that carried them. The plant sense came first — those neat green cases splitting open to spill peas — and English happily stretched it to anything snug and self-contained. The animal-group sense (a pod of whales or dolphins) is a separate, later, and genuinely murky thread: nobody is quite sure how a seed-case lent its name to a cluster of swimming mammals, so the honest answer is that this one's origin is uncertain.