There are many definitions of religion. Some are so broad they'd include your neighborhood garden club. Others are narrower: your garden club would need a deity, enthusiasm for that deity, and a set of beliefs and practices. We all have some sense of what religion means to us, but when we start talking about it -- trouble!
If you search "world religions," you'll find "Buddhism" on every list. Does that make Buddhism a religion? Does it mean that because I'm a Buddhist, I'm "religious"? I can argue that Buddhism is a science of mind -- a way of exploring how we think, feel and act that leads us to profound truths about who we are. I can also say that Buddhism is a philosophy of life -- a way to live that maximizes our chances for happiness.