Behavior-Driven Development (BDD), as its name indicates, is not a testing technique, but rather a development strategy (as well as TDD, which is Test-Driven Development). What it proposes is to define a common language for the business and the technical team members, using it at the outset of development and testing, which is why it's important for testers to understand BDD.
BDD and TDD
I used to think about BDD as an evolution of TDD, but then I realized that it is much more than a simple evolution. It's a different approach that solves a different problem. In TDD, the focus is on the unit test, while in BDD, the focus is testing on a higher level, functional and acceptance testing, as its aim is to comply with the business and not just with the code.