Debbie Michaud said it best in her book The Healing Traditions and Spiritual Practices of Wicca, “Wicca is a Pagan religion, but not all Pagans are Wiccans.”
This is a clean, and simple explanation. If you're a bit unsure of what she means, that's fine! Let's break this down...
Wiccans are Pagans; Not All Pagans are Wiccans
The reason a Wiccan is a Pagan (but not all Pagans are Wiccans) is because in order to be a Wiccan, you merely have to practice religion of Wicca. In order to be a Pagan, your religion must be outside of main world religions like Christianity.
Are "Pagans" Polytheists?
The term “Pagan” comes from the Latin word pagus (meaning “villager” or “rustic”), and paganus (meaning “citizen” or “civilian”). This term was originally used to describe those who were non-Christian, or part of Christ’s army.
Pagans are not automatically defined as someone who is monotheistic or polytheistic, but someone who practices outside of Christianity. Today, many Pagans may be Earth and Nature-centered in their worship (like Wicca). Others may not.
“Pagans may be trained in particular traditions or they may follow their own inspiration. Paganism is not dogmatic. Pagans pursue their own vision of the Divine as a direct and personal experience.”
For nature-centered worshipers, they may believe in a God and Goddess (which makes them polytheistic pagans). If you’re like me, you may have a nature-based faith, BUT worship in one God. That makes you a Pagan, but a monotheist Pagan.
Understanding the meaning and history behind words is important for those looking to learn about world religions. It is easy to lump them together in one category, but you miss so much rich history when you do that. When taking the steps into learning something new, make the time to learn about the history, terminology and antiquity.
 Oxford Dicionaries, s.v. “Pagan,” accessed Sept., 2017, https://en.oxforddictionaries.com/definition/pagan  Georgetown University, s.v. “Paganus,”, accessed Sept., 2017 http://faculty.georgetown.edu/jod/paganus.html  Georgetown University, s.v. “Paganus,”, accessed Sept., 2017 http://faculty.georgetown.edu/jod/paganus.html  Pagan Federation, accessed Sept. 2017, http://www.paganfederation.org/what-is-paganism/  Greek Mythology, accessed Sept. 2017, https://www.greekmythology.com/Other_Gods/Pan/pan.html