This is short for *Lamborghini.
It is a term used by those who engage in market speculation. This can apply to stocks but became especially popular for cryptocurrency. It is the dreams of massive wealth generation through price appreciation of assets held.
The idea that one is going to enjoy massive gains. The attitude becomes prevalent during the euphoria that is common in bull markets. People think whatever asset they are holding is going to moon, providing them with enormous returns.
This is the concept of "Lambo" which is also tied to mooning, the idea that prices will skyrocket.
Much of this stems from the early Bitcoin days. There were a number of millionaires created from the early buys (or mining) of BTC when the price was low. Being a HODLer meant portfolios garnered outsized returns that produced generational wealth.
Throughout the history of cryptocurrency, there were severe pullbacks. Bear markets often mean a drop of more than 70% in Bitcoin and 90%+ in altcoins. This drawdown can be painful causing the strong ones to HODL.
The popping of bubbles is a natural part of market movements. When the prices move too far, reversals happen The clearing out continues until there are few left to sell. It is at the nadir when another bull can start.