The literature on transfer learning has gone through a lot of iterations, and as mentioned at the start of this chapter, the terms associated with it have been used loosely and often interchangeably. Hence, it is sometimes confusing to differentiate between transfer learning, domain adaptation, and multitask learning. Rest assured, these are all related and try to solve similar problems. For the sake of consistency throughout this book, we will adopt the notion of transfer learning as being a general concept, where we will try to solve a target task using source task-domain knowledge.