What is the meaning of Fanum?

The site of an Ancient Roman temple or shrine.

fanum

shrine, temple, sanctuary, place dedicated to a deity

as a declinable word to introduce a placename named after a Saint, e.g. Fanum Sancti Iohannis for the various places named Saint John('s), San Juan, etc.

dative plural of fana

fanum

Source: wiktionary.org