Waves is a platform that permits other cryptocurrency tokens to be created. It is open source, and works via a blockchain, in common with many other cryptocurrencies. WAVES is the currency used on the platform, and this is limited to 100 million WAVES. The limited nature of the currency means it will have greater value than if it could be generated infinitely.
Therefore, when you see WAVES in capitals, you will know this is the currency itself that is being referred to. You can also mine WAVES if you wish and check the latest price on the official Waves Platform website. Just under 200,000 wallets for the currency had been created at the time of writing.