It is a non-innovative altcoin. Usually, it is just the next fork without any useful technological solutions. Such coins have small capitalization, and often they are not even listed at the exchanges.
Many enthusiasts are buying shitcoins in the hope of their unexpected growth and the opportunity to earn on speculation. For example, the creator of the site 66shitcoins.com in January 2018 bought 66 of the cheapest and questionable coins for $800 for the sake of experiment, and after a month and a half, the value of his portfolio fell to $388.
But in general, we can use the word shitcoin to call any coins that we do not like.