They're points you can use with the services offered by pixiv.
You can use them to send shoutouts on pixiv Sketch LIVE.
(* Between April 1st, 2009 and November 1st, 2015, there was a point system offered under the same name but it has since been terminated. These points cannot be used. On July 12th, 2018, pixiv began offering a new Points system compatible with all of pixiv's services.)