A designation from Level I to Level V describing how much trauma capability a hospital has. Level I has full surgical specialty coverage available at all times; Level V provides initial evaluation and transfer.
Why this matters to you
For severe injury this matters more than any star rating. A Level I or II centre can get a trauma surgeon into an operating room immediately, which is the thing that determines outcomes after a serious crash or fall. Emergency services route major trauma to these centres for this reason — which is also why you should call 911 rather than drive yourself.
Official source
The authoritative definition and current rules are published here:
Rules and figures change. Where this page and the official source disagree, the official source is correct — and we would like to know, so please tell us.