Ethereum is open source platform for decentralized application or distributed application (Dapp), in detail https://ethereum.org
Ethereum network is peer-to-peer network or decentralized network. Ethereum network is defined in detail in yellow paper (https://github.com/ethereum/yellowpaper) and white paper ( https://github.com/ethereum/wiki/wiki/White-Paper).
Ethereum network has 3 different elements:
Bootnodes: help ethereum clients to find their peers. The address of a bootnode is called enode.
Nodes: all nodes in Ethereum network, but it does not participate in the consensus mechanism
Mining Nodes: to valid transaction and create new block
Ethereum Virtual Machine: this is a compiler and run smart contract
Ether is one kind of cryptocurrency like bitcoin. Ether is used to pay for transaction fees and exchange in cryptocurrency market (https://www.binance.com)
Consensus algorithm: Currently, public Ethereum use Proof of Work (PoW) and having a plan to change to Proof of State (PoS), Private Ethereum use Proof of Authority (PoA)
Solidity is a language programing for smart contract of Ethereum