HODLING is holding on to your investment regardless of the way the market is acting. The idea behind HODL is that average people are not great traders and cannot see the perfect times to sell or buy. Rather it is better to buy and hold because over time the entire market will grow and so will your investment.
The first use of HODLING came from a typo in a post in a bitcoin forum, bitcointalk.org, in 2013. What started out as a post about the merits of time in market and not timing the market became so much more when the original poster misspelled HOLDING as HODLING in the title. The comments section ran with the typo and it became a meme.
-- one post in the comments from the bitcoin forum
The idea of HODL spread from there to all of the crypto communities. Every believed in HODL because everyone believed in the value of crypocurrencies. While HODL may be a meme, the idea behind it stands; time is the biggest determinate of growth. The technology of concurrency and blockchain will define the future and the value of blockchains will increase. And if you want to be apart of that future ... YOU MUST HODL!!!!