Freemasonry is a worldwide fraternity made up of many different and independent Grand Lodges. Since Masonry is both an organisation and a philosophical system of degrees, the "top rank" in Masonry may refer to two different things. However, in both senses, the rank of Master or Grandmaster designates the highest- ranking Mason.
The fraternity of Freemasonry is composed of individual lodges. Further, individual areas such as states and countries each have a grand lodge which oversees the other lodges. Each lodge elects a Master, also known as a Worshipful Master, who is the highest-ranking official of the lodge. Within a grand lodge, the Master is known as a Grandmaster. The Grandmaster is therefore the highest-ranking Mason in a political sense.
Politics vs. Degrees
There are two ranking systems to account for when discussing Freemasonry. One is the political ranking of lodge officers such as the Treasurer, Senior Warden and Master. The other concerns the ranks given out as part of the symbolic philosophical system of Freemasonry. While lodge officers obviously participate in granting the ritual degrees of Freemasonry, the political ranks and symbolic ranks are essentially two different things.
The core of Freemasonry is known as the "Blue Lodge." The Blue lodge confers three degrees, namely Entered Apprentice, Fellow Craft and Master Mason. The third degree of Master Mason is the highest degree in Freemasonry. While appendant bodies award additional degrees, these degrees are viewed as supplemental to the third degree and not as higher degrees per se.
Appendant bodies such as the York Rite and Scottish Rite award additional degrees to members that achieve the third degree of Master Mason. The York Rite awards a series of ten degrees, while the Scottish Rite awards a series of thirty degrees leading to the 33°. The 33° is an honorary degree that the Scottish Rite confers on selected 32° Masons. Again, all appendant degrees are supplemental to the Master Mason degree.