Paganism is any indigenous religion, that has just grown in a community rather than being founded like Christianity or Islam. I ought to add that this is an academic definition. Many people, particularly in the USA, say "pagan" when they ought to say "neopagan". Neopaganism is any religion of modern origin (like Wicca or Pagan Druidry) which aims to be compatible with traditional paganism.
Pagan religion doesn't have creeds or denominations. Pagans in different areas may worship different gods, but they don't deny the existence of each other's gods. A Christian could not worship in a mosque as they could not make the Muslim profession of faith, but as a Hellenic pagan I could worship with Chinese, Japanese, Indian, or African pagans with no problem at all. Our worship is also similar. The evening ritual I'll shortly be carrying out would not look odd to any Chinese or Indian. The offerings of fire, incense, food, drink, and prayer is much the same for all of us, and our altars have similar items, including images of our gods. My practices are also based on those of my ancient Greek predecessors. I keep many of the same festivals and sing some of the same hymns.
To see what Hellenic Polytheism looks like in Greece today
LABRYS : Hellenic Polytheistic community
For a thread in which I discuss my beliefs
Why be a Hellenic Pagan?
As a reconstructionist, I'm not a slave to a lifestyle: this is a religion, not a historical re-enactment society. The real slaves to lifestyle are Christians, Jews, Muslims, Sikhs, etc. "Don't eat pork, don't shave, do shave, cover your head, etc, etc."