I believe that "wintergreen" itself is a specific kind of plant (which has herbal pain-killing properties) but the word can also be used to unspecifically describe a plant which has green leaves in winter.
- I use wintergreen leaves steeped in hot water when I have a headache.
- I don't know what that plant at the end of my garden is but it's a wintergreen. It looked beautiful in December.
- I don't want my garden to look drab for six months of the year so I have planted plants which have wintergreen leaves.
This is a strange coincidence because I don't think I had thought of this word/plant for years until yesterday when I had a long conversation about it with a customer in the shop I work in and a friend who is keen on gardening. It's odd that your question should come up now.