In the abbreviation “XOXO” used on Valentine’s cards, the letter “X” represents a kiss.
The expression XOXO is commonly read as “hugs and kisses,” with X standing for kisses and O for hugs. It is usually placed at the end of a letter, message, or card to convey affection, friendship, or warmth.
The exact origin of these symbols is uncertain. One theory connects X with the Christian cross, which people historically used as a mark of sincerity and sometimes kissed as part of an oath. However, there is no definitive proof for that explanation, and the meaning of O as a hug is even less certain.
The Oxford English Dictionary records 19th-century evidence for X marks representing kisses. XOXO is therefore a conventional expression rather than a strict acronym: the letters symbolize gestures, not the initial letters of “kiss” and “hug.”