Streamlining is shaping an object in a way that it will reduce the resistance to motion. This is the way aeroplanes are shaped so that they can pierce through the air with less resistance. The best example of a streamlined creature is fish, which enables it to move in water more smoothly.
1 Additional Answer
Streamlining is a general word that is used to express the idea of making something as simple and effective as possible. Streamlining is meant to ensure that a body/idea/substance receives as little resistance as possible.