HODL originally came from a misspelling of the word “hold” on an online Bitcoin forum, and later turned into a whole culture in the cryptocurrency market; a strategy in which an investor holds their asset for a long period and avoids reacting emotionally to daily price swings.
This approach is usually set against “active trading,” in which a person uses technical analysis to profit from short-term fluctuations. HODL rests more on the belief that a project's true value will reveal itself over the long run, though this strategy isn't risk-free either and still requires choosing the right asset from the start.