"Hatha" is an umbrella term that covers the fundamentals of yoga, specifically developing an understanding of how your physical body works, and how your breathing can affect your state of mind. 

If a class has the word Hatha in the title you can expect the class to focus on straightforward held postures, some deep breathing exercises, and some delicious stretching. 

It's can be one of the most gentle forms of yoga and is ideal for beginners.

You won't get sweaty, but you'll leave feeling relaxed, well stretched, and with a spring in your step.