I get asked this a lot by family members when I tell them I am a Pagan. It is difficult to define in the sense of dogma as there is none to Paganism. Some forms have practices, but for the most part Paganism is very personal to each individual.
I tell them a simple answer: Paganism is about nature and our relationship to it. How we define it is personal as is how we define what Deity is. Mother Earth and the care for her is upfront for many Pagans and we look at nature as being part of us.
Most Western religions seem to ignore nature for the most part. Many say they don't care what happens to Gaea as they are going to Heaven anyways.
I see Mother Earth as a place of beauty which we must protect and honor. Reincarnation is part of this process, so we have to take care of our home for future use (my personal view).
Other Pagans might have differing views and are welcome to share theirs.
Another question I get: Is Wicca and Paganism the same thing?
Answer: Yes and no. Wicca is a form of Paganism, but not all Pagans are Wiccans. The same can be said of Christianity as all Catholics are Christians, but not all Christians are Catholics.