A blockchain is a decentralized network of computers around the world where all have exactly the same copy of the database of accounts, balances, smart contracts, NFTs, dapps, and other crypto assets.
Emerald Wallet is an app that may be used to create accounts and manage your assets on those blockchains, but it is not a blockchain in itself. It is just a user interface to send transactions to the blockchains we support.
Blockchains are sometimes called "public networks" because they are permissionless and anyone in the world can download the protocol to a machine and start running it to be part of the blockchain. All the computers in the world that participate in a blockchain run exactly the same protocol as well!
Miners and Stakers
Of all the participating machines in a blockchain, a subgroup of the machines may be miners or stakers. Miners or stakers are the ones that accept new transactions put them in a block and send the blocks to the rest of the machines for verification.
The machines that are not miners or stakers have the role of verification that the blocks and the transactions inside them are correctly formed by the miners or stakers. Once they verify this, they include them in the database.
Why Are They Called "Blockchains"?
Because the way in which new transactions are included in the database is by adding the blocks of data created by miners or stakers, these networks are called "blockchains" as the blocks form a chain of data as time passes by. It is just the way that new data is included.
In blockchains such as Bitcoin these new blocks of data are added every 10 minutes and in networks such as Ethereum or Ethereum Classic they are included every 15 seconds.
Proof of Work Blockchains
These are the networks that use miners to create blocks. The term "miner" is just an analogy to gold miners as these cryptocurrencies are considered "digital gold".
Miners use a lot of computing power and electricity to create the blocks and this work generates a cryptographic stamp that is added to the block. This cryptographic stamp is called a "proof of work", hence "proof of work blockchains".
Miners are paid a reward in the native cryptocurrency for creating blocks this way.
Proof of Stake Blockchains
These are the networks that use stakers who put money in the native cryptocurrency inside the blockchain instead of using computing power and electricity to earn the right to create blocks. The term "staker" is just because the assumption is that they are trustworthy because they have a "stake" in the network.
Stakers are paid a reward in the native cryptocurrency for creating blocks this way.