The definition of "altcoin" that I'm working with is: anything that is "bitcoin-like", but which is not bitcoin. (in other words, an ALTernate COIN).
Point well taken.
I see the main difference between Bitcoin and an altcoin is that you can exchange fiat currency for bitcoin on exchanges like coinbase, BTC-e and others.
I do not see that with the altcoin exchanges. On Mintpal, poloniex and a bunch of others, you can exchange altcoins only using BTC.
And so, I was using the "bitcoin--like" expression to actually mean a coin that can be exchanged with fiat currency.
I should have been more clear
than you need an exchange that accept fiat for whatever coin you want to support. A lot of exchanges are crypto/crypto ( in/out) but most allow fiat deposit to buy altcoins
