They refer to the number of posts you have in the corresponding tag, as well as the score you got with answers to questions that use that tag. For example looking at your profile right now shows:
- debian score: 17 posts: 14 posts: %18
- linux score: 16 posts: 17
As you can see only the first one, which is the tag you invested the most time into, shows the percentage of posts you have written with that tag compared to your total amount of posts. 14 posts are 18 percent of 77 posts, which is the total you get when adding the amount of answers you have posted and the amount of questions you have posted. Those are at the top right corner of your profile, which I linked to above.
Just to further illustrate: you can find all posts from you that are related to the tag "debian" with a search, which gives you 14 results. Of those 10 are questions and 4 are answers, so it also takes into account answers you have written to questions that use that tag, not just questions you have asked with that tag.
Looking at my own profile it looks like it only ever shows the biggest one with percentage and only once you have written posts with a handful of tags so that they can't be displayed properly anymore, so only when under the tag lists you can find the entry "View all tags", which would take you to [your personal complete list of "score in tag" "tag name" "x amount of of posts in this tag".
You can also see that the score only takes into account the answers you have written, not the question scores, even if the questions are included in the "Posts" and "Posts %" statistics. You only have four answers, which makes it easy to check that those scores add up to "17", while questions such as Linux - display or upgrade security updates only using apt with a score of "11" are not included.
Thanks to Jeff Schaller for pointing out in his comment that there is more information available when hovering over the grey block that contains the tag and the information asked about in this question:
There's also more information in the hover text ("Gave X non-wiki answers with a total score of Y")
This shows that the score and "amount of posts" only refers to non-wiki answers / questions.