Ethereum Classic
For a time, there was Coke Classic and New Coke. There are classic cars. Classic movies. Classic anecdotes.
Basically, the old, established version of something is considered the "classic" version. In this case, we're talking about Ethereum, which is a cryptocurrency, like BitCoin.
Ethereum Classic represents the old-school version. Old school, in this case, meaning before 2016.
In 2016, the people in charge of Ethereum decided to make a change in the code. The kind of change is known as a "hard fork"...a big alternation. Some people didn't like the change and stuck with the old version.
So there's the cryptocurrency known as "Etherium," which has the change. And then there's Ethereum Classic, which keeps the old version.
People who like classic movies don't like films made after about 1975. People who like Ethereum Classic don't like the version of the cryptocurrency that came after 2016. Same basic idea.