Dynamic is a secure exchange, where you can buy and sell BTC and ETH with your credit card in any currency, withdraw funds and buy cryptocurrency instantly.

Ether is the name of the currency used within Ethereum.

Ether is a necessary element -- a fuel -- for operating the distributed application platform Ethereum.

It is a form of payment made by the clients of the platform to the machines executing the requested operations.

To put it another way, ether is the incentive ensuring that developers write quality applications (wasteful code costs more), and that the network remains healthy (people are compensated for their contributed resources).