Albert G. Mackey explains the origin of the name "Freemason."
Albert G. Mackey, A Lexicon of Freemasonry (Philedelphia: Moss, Brother & Co., 1859), 159
FREEMASON. The word "free," in connection with "Mason," originally signified that the person so called was free of the company or guild of incorporated Masons. For those operative Masons who were not thus made free of the guild, were not permitted to work with those who were. A similar regulation still exists in many parts of Europe, although it is not known to this country. The term appears to have been first thus used in the tenth century, when the travelling Freemasons were incorporated by the Roman Pontiff. See Travelling Freemasons.