A Hodler is a true believer in cryptocurrency.
The term started with the bitcointalk.org community, one of the oldest public discussion forums focused on the Bitcoin ecosystem, blockchain technology, and cryptocurrencies, that is frequented by developers, investors, and technology enthusiasts.
Hodlers are long-term holders of a cryptocurrency, who buy and hold regardless of price.
They believe in and are confident of the long-term vision of their cryptocurrency of choice, whether that’s bitcoin (BTC) or another altcoin.
While they may not necessarily understand the technical merits of a cryptocurrency, they at least believe in the long-term value of their investment.
“Never-sellers” on the other end, never sell, regardless of market volatility or any decrease in the value of their cryptocurrency bags.
Some crypto market participants believe hodlers are just plain crazy, leaving profits on the table by never selling at market tops or ATHs.
See HODL for more info.