Literally 'name not seen in the classics' (经传 = the Confucian classics 经 plus their commentaries 传). The phrase originated as a way to dismiss someone whose name was nowhere in canonical literature — i.e. a person of no reputation. Today the 'classics' framing is metaphorical: it just means 'never heard of'.
usage
Almost always used as an attributive ('a 名不见经传 X') or predicate to set up a contrast — the obscure person/company then does something surprising. Pairs naturally with 居然 (jūrán, 'actually, surprisingly') or 却 (què, 'yet').
