A sticky post in WordPress is one that stays at the top of the page no matter what gets posted after that. This is useful for a post that you want to highlight or for an announcement.
Way back the best way to make a post sticky was to fudge with the date – I would make it a date way in the future so it would stay the top post.
Then the WP-Sticky plugin was created, which allowed me to make a post sticky and gave me some control over styling. For example, if the sticky post is an announcement, I don’t want the date to be included because then it looks like a regular post.