What is the difference between a world record, an Olympic record and a national record?
The population of performances each is drawn from, and the conditions under which each may be set — which is why they can differ substantially and why an Olympic record is frequently slower than the world record.
World record. The best performance ever recorded anywhere, by anyone, under conditions meeting the governing body's requirements for ratification. Available to be set at any eligible competition.
Olympic record. The best performance at the Olympic Games specifically. Because the Games occur every four years and conditions there are not always optimal, the Olympic record in many events lags behind the world record — sometimes by a considerable margin. Championship records work the same way for World Championships and continental championships.
National record. The best by an athlete eligible to represent that nation, set anywhere.
Other categories: area or continental records; age-group records (junior, under-20, masters by five-year bands); indoor records, kept separately because conditions and track geometry differ; and world bests — a term used where an event exists but formal record status does not apply.
What ratification requires, and why performances are sometimes rejected:
An approved venue and equipment, with certified measurement of the track or course.
Approved timing, fully automatic for track events.
Wind measurement within limits for sprints, hurdles and horizontal jumps.
Doping control immediately after the performance. A record will not be ratified if the athlete was not tested, which has invalidated genuine performances on administrative grounds.
Competition conditions — records generally require a properly organised competition, not a solo time trial, which is why some high-profile assisted attempts are recorded as "best" rather than as records.
Road running has additional requirements on course drop and on separation between start and finish, to prevent downhill or wind-assisted courses producing unrepresentative times.
Records can be removed retrospectively following doping sanctions, and several long-standing marks have been annulled years later — which is why the record book is not a stable historical document.