Habituation is what happens when an organism gets used to a certain environment or stimulus. Through habituation, the squirrels in a city park often become so used to humans that they don't run away from them — and even beg them for food.
If you live near an airport and hear planes taking off and landing every day, habituation occurs — eventually you get so used to the noise that you don't even notice it. The same thing happens to non-human organisms. Thanks to habituation, your pet turtle doesn't hide in his shell every time you touch him anymore. He is used to you petting him. When the world presents a new stimulus, habituation can help an animal adapt to it. Habituation comes from the Late Latin habituat, "accustomed."