iRacing uses a system where there is a minimum participation amount in order for races to go official. This is done to prevent people from picking a nearly empty race (for example at 3am at night at an unpopular track & car combo) and simply winning since there was a lack of competition.
You will often see people refering to races or events going 'official'. They are simply referring to that particular event or race having enough participation so that the player can earn iRating, Safety Rating and Division Points. Ultimately going official means that the result matter. If the race doesn't go official, due to a lack of participation, then no iRating, Safety Rating or Division Points are earned.
" The minimum number of drivers for a Ranked Race is typically set at 6 drivers, but this is a guide and not a rule. "iRacing Sporting Code - Section 6.3.1 Field Size
It's usually safest to pick a racing series that has a high level of participation to make sure your racing results actually move the needle.
Want to learn more about out which series are popular and go official often? Check out