The words in between the tags will show up as a link in the web browser (usually a different color, boldface, or underlined) and clicking on it will bring your reader instantly to wherever the anchor tag with the name "TOC" is located.
Obviously, if there were more than one anchor tag with the name "TOC", it would get confusing.
In this case, "TOC" corresponds to "Table of Contents".
This page gives an overview of all articles in the 1911 Brittanica which are alphabetized under Toc to Tou.
Diem Lanzaeanum, which last has a very wide toc range in time; Monocotyledons, by a Sabal and a feather-palm, as well as by the two aquatic genera above mentioned; Gymnosperms, by the extinct araucarian genus Doliostrobus, by rare pine-cones, and by Athrotaxis.