Anything you spend money on can be thought of as an investment. The investment is both in yourself and in whomever made the product. If you spend money on a movie, you are investing in entertainment for your own well-being, perhaps (to take your mind off things), as well as in the studio that brought you the movie.
That said, we often don't think of our regular expenditures as investments, and doing so could change our way of thinking about how we spend money. When we are weighing whether or not to purchase thing A or thing B, considering the potential ROI on our investment might help us decide.