One of the best definitions and most complete resides on the website of the Grand Lodge of Oregon.

The link to the definition of Freemasonry on the Oregon Grand Lodge website is:

What is Freemasonry

Feel free to explore the Grand Lodge website.  It will give you a greater sense of what the Fraternity is and does.

Another excellent site of interest is:

www.askafreemason.org.

Three of their "Ben Franklin Chats" video's are shown below.