Bandha is the Sanskrit for bind. In the context of Asana in Hatha Yoga it is refered to as a lock. It is pronounced almost like "bann'da", (the 'a' at the begining sounds like 'a' in "law")
If Hatha seems unchallenging or boring to you, you haven't been introduced to the practice of bandhas. The bandhas add depth and a sense of the profound to a Hatha practice. Bandhas are a way to absorb prana and bind it in to the body. Each Asana, coupled with certain bandhas, then becomes a unique receptacle for absorbing prana.
Best to learn more about the bandhas after one has been properly introduced to Hatha Yoga and has been practicing for a while. Reasons are to avoid internal injury and overcomplication. Different teachers from different styles view them somewhat differently, i.e. use them right from the start; name them differently from other styles; don't incorporate them at all. The bandhas must be learned from a proper teacher to make sure the student is not making any mistakes.
Related: Hatha Yoga | Asana | Pranayama | Raja Yoga | Hatha Yoga Pradipika | Yoga Sutras