Blended learning is a phrase that is used to describe a few different scenarios, which all boil down to one end result: A learner uses a mix of learning tools and techniques to improve their knowledge and skill.
For example, blended learning may be a combination of eLearning and classroom with perhaps an addition of some hands-on practice. Learning to drive a car is always a good scenario to use to describe other forms of learning, so let's start there:
Learning the rules of the road can be done through books or online and is usually a combination of both. Learning how the car functions can be learnt from a book initially, but getting your hands on the wheel and feet on the pedals is usually considered the best way of learning 'how' to drive a car. The learning from books, in class and online can be set by your instructor, or you may find your own resources. Practice combined with more learning about the rules is the key to becoming competent as a driver.
Blended Learning is as simple as the phrase first implies - a combination of learning techniques which when blended together produce the best result.