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It is your reputation. New people start at 25 and then it can grow by gaining upvotes from people with higher reputation (if I remember this correctly). It can also go down if you get flagged by people with higher reputation. At the lower numbers, it'll grow faster. The higher you get, the slower your progress becomes. I've come to the point where it feels like it is not growing at all anymore :-)

Aaah thanks, that's making sense now, not sure if I was 37 or 47 before, but I'm 40 now, hopefully it's only gone up and not down. :o

As long as you don't get flagged (which is basically a downvote), you're safe. Just stick to original content (no plagiarizing) and don't be insulting without good reason, that way you won't attract a flag! I'm sure you were 37 before. Can't imagine you lost any :D