A small, self-standing structure such as a newsstand or ticket booth.  The original kiosk had room inside for a person who handled the transactions; however, the term evolved to refer to unattended self-service booths with computers that dispense information or make sales via a touchscreen.
Other than simple soda or candy machines, almost any modern vending machine that accepts credit cards can be called a kiosk.  For example, digital photo kiosks are today's counterpart to the earlier, manned kiosks for analog film developing.  Accepting memory card or CD/DVD input, they allow users to select images and perform limited editing.  The units can make prints on the spot as well as burn them onto a CD.  See 
self-service application and 
touchscreen.
The Photo Kiosk
Photo kiosks with touchscreens have popped up in shopping malls and venues worldwide.
Tablet Kiosks
The flexibility of a tablet makes them ideal for kiosk use.  Armodilo Display Solutions makes a variety of desktop and free-standing housings that securely hold Apple, Android, Windows and BlackBerry tablets.
Self Service
Any stand-alone self-service unit can be called a kiosk, such as this parking ticket dispenser in Philadelphia, which accepts cash and credit cards.