Probably most literally translated as "Please" accompanied by a palm-up hand gesture. Commonly used in shops in place of "Hello, can I help you?", but it can also mean "What's wrong?", "Pardon?", or "Do you understand?", and a vast array of other context-sensitive things. It definitely has other nuances that I haven't grasped yet, as I am fairly new to the language. [Wiktionary entry](http://en.wiktionary.org/wiki/tess%C3%A9k)
You can apply the German “Bitte” in the same situations