HODL is a term commonly used by cryptocurrency investors that refuse to sell their cryptocurrency regardless of the price increasing or decreasing. It is more frequently used during a bear market when people refuse to sell their coins despite the price drop. 

HODL was later retrofitted to be an acronym (backronym) for “Hold On for Dear Life” and refers to not selling, even during strong market volatility and poor market performance.

Origin of HODL:

HODL was originally a spelling mistake by a user named ‘GameKyuubi’ on BitcoinTalk. In the original BitcoinTalk thread titled “I AM HODLING,” GameKyuubi wrote:

I type d that tyitle twice because I knew it was wrong the first time.  Still wrong.  w/e.  GF's out at a lesbian bar, BTC crashing WHY AM I HOLDING? I'LL TELL YOU WHY.  It's because I'm a bad trader and I KNOW I'M A BAD TRADER.

HODL has since become a strategy used by people who admit they do not have the skills to do short-term trades - such as scalping, day trading, or swing trading. The term HODL has also inspired the creation of a similar term often, BUIDL, which is commonly used by the cryptocurrency community to refer to the many kinds of applications that are being built within the blockchain industry.