The story
Explained as a phonetic rendition of see facts. An earlier electromechanical system was called BEEBFAX: see Beeb and fax.
Etymology from Wiktionary, CC BY-SA 4.0.
Ceefax
Today it means: A simple information retrieval service offered by the BBC from 1974 until 2012, whereby "pages" of information are delivered sequentially to a television set and the viewer can move between them. Full definition →