I believe that for a Bitcoin maximalists any altcoin is shitcoin, like some others mentioned. They believe only in one cryptocurrency and don't recognize accomplishments of others. I am not one of these people, so for me a shitcoin is a crypto with no special features and use cases, usually with a small community of supporters, decreasing price, availability only on small exchanges and low market capitalisation. A coin does not have to possess all of the mentioned qualities to be considered one.