The term refers to when people start buying an NFT without doing much research.
The Long Explanation
In the NFT world, the term is used to describe a person or people when they buy a non-fungible token shortly after the particular NFT project was launched, without performing proper research.
Apeing is effectively ingrained in NFT enthusiasts’ fear of missing out (FOMO). They see an NFT project being launched and see a ton of people on Twitter or Discord talking about it. This triggers their fear of missing out on a potential project that could skyrocket in value and entice novice investors to jump in and purchase.
While some of these could be legit NFT projects, many could be scams as well, and people getting financially irresponsible in a project like this or without knowing a lot about it.
“I just aped in X project” is a common way of using the term in a sentence.