It is a Music Dictionary site. You may choose any letter of the alphabet listed at the bottom of the home page. Clicking on the alphabet you want will give you a list of all the terms starting with that alphabet in a panel on the left. For example, if you click "A", you will get musical terms like Adagio, Allegretto, Andante, Andantino etc listed on the left panel.
If you want to look up "Adagio", clicking on the word will give you its definition plus an audio of how it should be pronounced plus the spelling as we know it in English terms (Ah-DAH-jio).