A sticky is a thread post marked as a permanent entry within a Sub-Forum. Important points or information posts can be/have been marked as a sticky so the thread remains at the top of all threads in a sub-forum. Any new posts in a sub-forum will follow all stickys in that group. An example of a sub-forum is "Powder Coating Questions" as seen here:
Powder Coating Questions - Plating Powder Coating Buffing Anodizing - Caswell Inc. Metal Finishing Forum
The stickys are marked "Sticky:" preceding the thread title.