It is most commonly found in athletic sports, such as track and field, other forms of running, swimming and weightlifting.
The term came from the world of running, referring to a person's best time in a race of a specific distance.
If they run faster than 28:45 in a subsequent 5K race, then they have a new PB for that distance.
[1] Over time, PB came to mean any new record in a sport that could be performed by a single person.
Although the term "personal best" is increasingly used in official sports statistics, it can also refer to an unofficial best individual performance.