Wicca is an earth-based mystery religion, which was formed from various sources (Thelema, Golden Dawn, The Goetia and Clavicula Salomonis, as well as native British and European religions, such as Celtic practice) in the (estimated) 1930's - 1940's and brought into the public eye by Gerald Gardner with the publication of his "fiction" work, High Magic's Aid in 1949, published under the pseudonym of Scire. In 1954, following the repeal of the Witchcraft Act in England, he published a further work, namely Witchcraft Today. Thus the religion was brought firmly into the public eye.
Wicca in it's original form is an initiatory, Mystery religion, which is oath-bound, practiced in a coven and is a priesthood. With the rise in popularity of Wicca through popular culture and the increase in publications on the subject, it is now fair to say that there is Wicca and a number of paths based on Wicca. Wicca itself remains the initiatory form and the latter comprises those paths inspired by the first form, which are not necessarily initiatory but are often solitary or eclectic and often involves a self-dedication ritual by the practitioner to their chosen deities.