Toastmasters International is a worldwide organization with nearly 16,000 clubs and over 345,000 members. It is best described by Toastmasters International itself at its  website. It is often abbreviated as "TI". It should not be confused with World Headquarters, which is the principal place of business, employing (as of 2016) over 100 people.
The organization's guiding documents are its Governing Documents.
Toastmasters was founded by Ralph C Smedley.
See also Toastmaster, for a discussion of the various ways the words "Toastmaster and "Toastmasters" may be used.