A derogatory term used to describe altcoins that are based on faulty technology or have little promise for the future.

A shitcoin can mean several different things. This is because the term shitcoin is a colloquialism in the cryptocurrency space. 

Originally the term shitcoin referred to any other coin besides Bitcoin. The term was warranted too, since as soon as Bitcoin began to gain popularity the cryptocurrency flooded with alternative coins which professed to be better than Bitcoin. 

Most of these coins failed to deliver on their promises, and thus the term Shitcoin grew in popularity. 

The polite term for shitcoin is altcoin. Altcoin stands for alternative coin and was often used by the cryptocurrency press to refer to every coin besides Bitcoin. 

However, as the cryptocurrency space grew over the years several alternative cryptocurrencies did deliver on their promises. The biggest ones so far are Litecoin -- which is a faster version of Bitcoin; and Ethereum -- which allows smart contracts to run on its blockchain. 

These cryptocurrencies and several others should not be considered Shitcoins, since they deliver on their promises and have quality use cases that differentiate themselves from Bitcoin. 

Nevertheless, some Bitcoin maximalists (people who believe only Bitcoin should and will survive), still use the term to Shitcoins to mean all coins besides Bitcoin.

So as you journey through the cryptocurrency space, be sure to apply the term shitcoins to only those coins that are scams and deserve it. Otherwise you might end up biased against alternative cryptocurrencies that might in fact become useful one day.