What is "treat" and what is a "vote" on the Rover page where I'm typing this question?

Treats are explained in the FAQ linked below:

https://www.rover.com/community/faq/

They're supposed to reflect contributions to this online community board. You are given 30 treats a day to spend, voting on answers provided by other members. There is a plus sign and a minus sign on the left. If you click on the plus sign, you will be giving another member here 10 treats, but only 1 is subtracted from your daily allocation.

There are several other threads about treats, which you may want to check out. Just do a search on "treats" or "voting."