ABA in a nutshell:
Applied behaviour analysis focuses on the principles that explain how learning takes place. Positive reinforcement is one such principle. When a behaviour is followed by some sort of reward, the behaviour is more likely to be repeated. Through decades of research, the field of behaviour analysis has developed many techniques for increasing useful behaviours and reducing those that may cause harm or interfere with learning.
Applied behaviour analysis (ABA) is the use of these techniques and principles to bring about meaningful and positive change in behaviour.