A common, useful, and sort of generic definition of learning:

learning - a relatively permanent change in behavior or in behavioral potentiality that results from experience :

relatively - because although the change should last some time, it needn't last forever (e.g., forgetting and extinction are allowed)

behavior - because any change due to learning must be observable in principle if it is to be studied scientifically, and behavior is observable

potentiality - because an organism may not have occasion to exhibit its modified behavior unless the appropriate circumstances arise

experience - because modifications of behavior due to developmental or physical causes (maturation, injury, fatigue, etc.) aren't considered "learning"