It means the total number of times the post has been read by everyone out there.
So the very first post will always have the highest number, say 302. The next one might have 297 because everyone who read the second post must have read the first post, but a few of the people who read the first post never came back to read the second post.
By the time we get to the 10th post, I think it means that you will have read the first post 10 times, the second post 9 times, the third post 8 times ... and the 10th post once. I'm sure there's some formula with lots of xs and ys to express it.