No, Bitcoin is not an Altcoin.
Altcoin is a shortened phrase for Alternative Coins (aka alternative cryptocurrency).
Altcoins are lesser known cryptocurrencies.
Bitcoin is just ONE type of crytocurrency, out of thousands. In mainstream news, Bitcoin is most heavily reported in the crypto world because it gained momentum and in turn, success.
To date, Bitcoin remains the most liquid leveraged markets of all of the cryptocurrencies.
Some of the more popular Altcoins are: Ethereum, Ripple, Neo and DASH.