Room:        The space a boat needs in the existing conditions while manoeuvring promptly in a seamanlike way.

Keeping Clear:  One boat keeps clear of another if the other can sail her course with no need to take avoiding action and, when the boats are overlapped on the same tack, if the leeward boat can change course in both directions without immediately making contact with the windward boat.

Also see ISAF case 50

A give-way boat did not keep clear if the ROW boat has-

“a genuine and reasonable apprehension of collision”