Simply said, Meditation Music is music that aids or accompanies the practice of meditation, or is alternatively used to meditate on.
It may have a specific religious content, being vocal or only instrumental, but it can also be non-religious or non-spiritual just used to induce a specific mood and ambiance.
The activity of listening to Meditation Music can aid in detaching a person from their surroundings and help them focus on their own thoughts and actions, or alternatively help them to focus only on the music to support a state of calm, mindfulness, visualization, and/or contemplation.
Yet, Meditation Music is also used more practically during day-to-day activities or to reach certain personal goals. Think of increasing personal awareness to help identify patterns of stress and anxiety, improving focus on present thoughts and actions, promoting addiction recovery, and reducing depression, anxiety and stress symptoms.
In the latter case, music is rather used as a coping mechanism, becoming an emotion-focused means to cope with unpleasant stimuli, aimed at reducing or eliminating the emotions that arise in response to stress.
In addition, when Meditation Music is used to cope with stress it also reduces the physical manifestations of stress, such as decreased heart rate, blood pressure, and levels of stress hormones.
At any rate, when music is used in a more structural and clinical way for health benefits, for instance by a therapist to treat a patient, the activity rather qualifies as Music Therapy.