What is the Olympic A standard?

The A Standard is the "automatic" qualifying time for an event. The B Standard is the backup qualifying time. To be guaranteed a spot in an Olympic event, you must both earn a slot from your country (number of slots may vary by event and by country) and have achieved the A standard. If there are not enough participants around the world who have qualified that way, then competitors with B Standard times may be added to "make the event competitive."