PR = Personal Record. a/k/a your fastest time for a particular race distance. Generally used for bragging rights outside of those who are truly competitive runners that stand to win real money at various races. However, that latter class of runner is a lot faster than I ever was, and is still a fair bit faster than exxxviii even if that individual is female. Want feel humbled? Check out the winning times for the Peachtree Road Race 10K.
Outside of prize money and bragging rights, a race time result can lead to being placed in a "better" starting corral for a future race. For the same Peachtree Road Race 10K above, this past year runners had to have a below 39:10 (m:s) 10K time to be in the "seeded" corral immediately behind the elite invited runners, and a 39:11 to 45:23 time to be in the next corral (A). The advantage of a "better" corral is fewer runners you need to dodge before the course starts to spread out, allowing you to run a slightly shorter distance, and thereby post a better time by a few seconds. Here's an illustrative article on tangents: http://www.runladylike.com/2014/09/24/running-the-tangents/
Race times can also be a qualifier to even get into some high-demand races, the Boston Marathon is one such race.
Outside of prize money and bragging rights, a race time result can lead to being placed in a "better" starting corral for a future race. For the same Peachtree Road Race 10K above, this past year runners had to have a below 39:10 (m:s) 10K time to be in the "seeded" corral immediately behind the elite invited runners, and a 39:11 to 45:23 time to be in the next corral (A). The advantage of a "better" corral is fewer runners you need to dodge before the course starts to spread out, allowing you to run a slightly shorter distance, and thereby post a better time by a few seconds. Here's an illustrative article on tangents: http://www.runladylike.com/2014/09/24/running-the-tangents/
Race times can also be a qualifier to even get into some high-demand races, the Boston Marathon is one such race.