Terminology is one of the best reference apps currently avaialable on the iPad: it’s great looking dictionary for the English language, which Cody reviewed a few weeks ago. Since then the app has been doing pretty great in the App Store, but what about actual sales figures?

The developer of Terminology helps us understand the situation.

“It did far better than I expected, topping out at #25 on the Top Overall Paid App charts for iPad, and holding the #1 position in the Reference category for a full week.

Though I’m thrilled with it’s performance, I was a little surprised to see what those rank numbers corresponded to in actual sales. Terminology is iPad only (for now!) and clearly there are not as many iPads in the wild as iPhones and iPod Touches — but, I imagined that #25 on the sales charts would translate to something a little more than 448 units/day.”

What do we learn from this? If you know you’re developing a good application for a category that’s not very crowded, make sure that a) the app is great and b) charge a premium for that. You won’t sell thousands and thousands of copies (you’re aiming at a very specific audience), but you’ll make some good bucks out of it.