How is that wrong?
It's not necesarilly created by an Admin.
To say created by an admin, would imply that all topics created by admins are sticky topics, and that topics created by non-admins can't become stickied.
And also change it from "A topic sticky-ed by an Admin" (Don't use the word you're defining in a definition).
Change it to something like:
"Sticky: Any Topic that has been 'Stuck' on the top of the topics board. These topics do not need to be bumped to remain at the top of the page.
