system
A chat on subreddit /r/pcmasterrace
human
Can I get an ELI5 of what that means/meant?

E: Probably shouldn't have said ELI5. I have a rough knowledge of how mining is and how you are being rewarded for verifying transations on the blockchain, just not how proof of stake changed things.
gpt
You're probably aware, at least on a surface level, what bitcoin is. Bitcoin is a digital currency that is acquired by a "proof of work" model. What this means is that bitcoin mints "coins" by producing a really long string of characters that your GPU has to guess. This is what people mean when they say mining. Each number guessed is a swing of the pickaxe, and every once in a while, you might get lucky and hit a rich vein of bitcoins. 

This is very oversimplified. For example, there are pools where you combine your "work" together to get a share of the coins.

Ethereum worked this way too. However, the plan was, once there's enough coin in the world, to switch away from this kind of "proof of work" system (i.e. mining) to a "proof of stake" system where you acquire new coin by "staking" your coin. Think of it like earning interest on coin that you've set aside and promise not to use. There are mechanisms in place to facilitate this, and I'm not smart enough to explain those to you.

This happened in September, and there's no more mining ethereum.

TLDR: Instead of mining ethereum, now you get more ethereum by staking the ethereum you already have.