Put basically, any religion with more than one god, otherwise known as polytheism. Usually nature based, but not necessarily in a hippy "flower power" way. The term Pagan is usually applied to the old European pre-Christian religions of the Greeks/Romans, the Germanic tribes (such as the Vikings, Saxons and Danes etc) and the Celtic tribes. Wicca is a more modern blend of Paganism, that includes elements of all the above religions. Pagans can be found in all walks of life, from the Hippies through to Neo-Nazi groups and all in between. This goes to show that there are many forms and beliefs within Paganism.
Anton LaVey's form of Satanism
includes many elements of paganism, almost an anti-Wicca.
Alot of Pagans attempt to hide their religion from their peers as pagans have been persecuted since the early days of Christianity, and as such some tend to have anti-Christian views.
That said, if they are known pagans, most pagans will quite gladly give time to help out people starting out on the pagan path and will talk to non-pagans about their views and beliefs.