Apeing is slang in the crypto community for buying a coin or token based on sentiment, often without thorough research. The term apeing itself comes from the animal species, ape. Additionally, apeing is another form of FOMO-ing into buying something.
Apeing should be avoided at all costs as it is most of the times used for buying memecoins. Influencers also use this term to induce FOMO towards their followers. As opposed to apeing, you should always DYOR before buying into something.