EOL stands for “End of Life,” which means that a vendor has decided that the product in question has reached the end of its “useful lifespan”. After a particular date the manufacturer will no longer be marketing, sustaining and (in most cases) selling the product in question.
In our case, most questions are about chipsets that aren't manufactured anymore. Therefore, after running out of the required (no longer manufactured) chipsets, some products will transition into an EOL status.