The number that you've highlighted here is the reputation score.
It's an indication of how a user is performing in the community based on the upvotes and downvotes that they have received.
The higher the number, the higher the number of upvotes they have received and so it is assumed that they are good contributors.
It is the opposite for those with low scores, which is usually indicative of a user's history of copying & pasting content or generally being offensive towards other users.
Everybody starts on 25 and this can go up to 75 or as low as -25.
Hope this helps.