IMO altcoins means they came out after the original one. But it doesn't mean they are not good! Many altcoins has improved a lot compared with the existing bitcoin. Or they supplement the functions of bitcion, like sidechain, colored coins etc.
I think this will be the only informative post in this thread. By definition altcoins are alternative coins to Bitcoin. It's simply slang that became accepted as a way to describe everything after Bitcoin. It doesn't mean altcoins are synonymous with "shitcoins". I mean that's like saying you can't call an electric company an electric company simply because General Electric came first. They are all electric companies, just as bitcoin and all altcoins are called the misnomer-ish name "cryptocurrencies".