EIP is an acronym for Ethereum Improvement Proposal. As stated on their website, these describe the standards for the Ethereum platform, including core protocol specifications, client APIs, and contract standards. In simpler terms, you can think of them as upgrades for the Ethereum Network.
ERC-721 is a token standard that allows for the creation of NFTs on the Ethereum blockchain.
Designed by Beeple, this piece of digital art is composed of 5000 images made by Mike Winkelmann over the course of his career. It is the most expensive individual NFT which was sold for $69.3 million.
A blockchain explorer is a software that is used for visualizing blocks, transactions and other network metrics such as transaction fees, hashrates, block size, block difficulty and the like.
If you’d like to familiarize yourself with explorers, you can visit some of the well known ones such as Blockchair, Etherscan, Viewblock.