Definition of St Valentine's Day noun from the Oxford Advanced Learner's Dictionary

St Valentine's Day

noun
ˌsnt ˈvæləntaɪnz deɪ
 
; ˌseɪnt ˈvæləntaɪnz deɪ
 
 
the day (14 February), when people send a card to the person that they love, often without signing their name on it