it depends honestly. You can be any religion and follow the philispohical path of Druidry. But Druidism itself is a religion. I think following either path, philisophically or religiously, makes one a druid. That is, have an utmost respect and reverence for nature, doing what you can to lessen your ecological footprint, celebrating the 8 stations on the seasonal wheel of the year, knowing the local flora and fauna in your respective ecological region and their importance, and practicing meditation to bring one together with the Solar and Telluric Currents of the world. My answetr does not necessarily reflect everyone's view though. As John Michael Greer puts it "Ask any 3 Druids the same question and you will get six different answers." Druidry itself is a very adaptable philosophy, based around ones own natural environment that you are working with. I recommend "The Druidry Handbook" by John Michael Greer for further reading if you are interested.