Definition: Not to be confused with mark-room.
The space a boat needs in the existing conditions, including space to comply with her obligations under the rules of Part 2 and rule 31, while manoeuvring promptly in a seamanlike way.
Rule 31: Touching A Mark: While racing, a boat shall not touch a starting mark before starting, a mark that begins, bounds or ends the leg of the course on which she is sailing, or a finishing mark after finishing.
Racing Rules of Sailing