Weather Sealing
Gaskets and overlapping construction that resist the entry of dust and moisture into a camera or lens.
In depth
Weather sealing is not waterproofing, and almost no manufacturer publishes an IP rating for it — the claim is resistance to splashes, dust and light rain, not immersion. It also depends on the whole system: an unsealed lens or an open card door defeats a sealed body entirely.
Examples in practice
A sealed body and lens keep working through an hour of coastal drizzle that would put an unsealed kit out of action.