There are various types of meditation, whether this be following the breath, to visualisation, to mantra meditation and so on. They all very much have a similar end point… to improve in body, mind or spirit or even all.
Many of the meditations relating to observing, whether this is the breath or a body scan, a visualisation or observing your actions or surroundings could be defined as meditation is an opportunity to access a level of wholeness for the body, mind and spirit.
This definition encompasses all the benefits of being present, letting go of mind and judgement or/and tension and thought, self-medicating, creating positivity and allowing you to problems solve.
Another definition could be Meditation is a daily and disciplined practice which connects you to the collectiveness and creates synergy by being present and having acceptance with no judgement.
A third example of a definition is A practice to strengthen the neurons in the brain through training the brain to become present and observe thoughts, feelings and beliefs.