Ether (ETH) is Ethereum's digital token, which is a cryptocurrency similar to Bitcoin. It has value within the market and it is used to facilitate the information exchange on the Ethereum blockchain. Developers who want to build DApps and users who want to interact with the smart contracts on the Ethereum blockchain are required to use Ether (ETH). Ethereum is also a smart contract platform, which provides transparent and trustable code execution. Many people build applications on top of smart contracts to allow users to have more control over their digital assets and information.
Cryptocurrencies are digital equivalents of currencies, where the record of every transaction is stored on a blockchain. Limitations and scarcity are imposed on the digital currencies to reflect the nature of real-world currencies, with sophisticated programming implemented to make it difficult to counterfeit the currency.
Blockchain is the underlying technology that supports cryptocurrencies. A public blockchain is a digital record of information that is duplicated and shared across a network of many computers instead of a single central server. Updating the digital record requires a complex computational process to ensure that only the right information is added to the blockchain. The public record of information stored across the network ensures that no one entity is able to control, corrupt and change the data, keeping the record secure and verifiable.
DApp stands for decentralized application. Like normal applications, they provide some form of service for users. However, parts of their code are written as smart contracts on the blockchain. This allows anyone to inspect the code for flaws, or unfair terms and conditions. By allowing part of the code to be transparent to the public, DApps allow users to have greater flexibility in how they manage their digital assets, and to ensure that the DApp operates responsibility.