Q: is AirPrint printer the same as a Wifi printer?

AirPrint must be "built in" on the printer in order to work with AirPrint on the iPad. It is like having built in print drivers to work with the iOS AirPrint feature.

Did you check to see if your printer is an AirPrint printer on the website that you posted your question in?

http://support.apple.com/kb/ht4356

If your printer isn't AirPrint compatible, you will need a third party app in order to use your WiFi printer.

A small addition to Demo's response, to answer your "What's the difference between WiFi and AirPrint?" ...

A WiFi printer is one that can perform over-the-air network operations.  It can reside as a device on your network along with your iPhone.  But iPhones, though they can "see" WiFi printers on the same network, may or may not be able to print to them.

An AirPrint printer must first of all be a WiFi printer.  But additionally, it is a printer which is compliant with Apple's protocol that guarantees compatibility to your iPhone.

As Demo says, there are third party apps out there that facilitate printing from many WiFi printers, but they tend not to be nearly as complete or feature-enriched as the AirPrint printer interface.

If your printer isn't on that list, you can look into the third party apps as mentioned. I use Print n Share, and I also seen printopia and printcentral recommended.

Also search for your printer manufacturer in the App Store. Some of them have come up with apps of their own.