A comparatively large hashrate makes Ethereum one of the more secure blockchains in existence.
A smart contract is simply a piece of code that Ethereum allows the development and deployment of these. It's called a contract because code that runs on Ethereum can control valuable things like ETH or other digital assets.
Ethereum Virtual Machine
Ethereum provides the underlying technology-the architecture and the software-that understands smart contracts and allows you to interact with it.
Decentralized applications (Dapps)
Ethereum allows you to create consolidated applications, called decentralized applications. A decentralized application is called a Dapp (also spelled DAPP, App, or DApp) for short.
Decentralized Autonomous Organizations (DAOs)
Ethereum allows you to create these for democratic decision-making. DAOs tackle an age-old problem of governance, which political scientists and economists refer to as the principal-agent dilemma. This occurs when the agent of an organization has the power to make decisions on behalf of, or impacting, the principal - another person or entity in the organization.