The term Transgender is one of the most all-encompassing terms in common usage both within the TG Community and in the mainstream.
In many cases the term is highly context-dependent in precise meaning.
There is no universally-accepted definition of the term "transgender" or related terms. There is no universal agreement as to what groups of individuals fall within this definition. Some individuals find the term "Transgender" to be an inaccurate descriptor of self-identity.
The earliest documented use of the term "Transgender(ism)" appears to be within an article in the Journam of Sexual Hygiene and Pathology in 1965 by Dr. John Oliven. The term may have been used episodically prior to this date.
The terms "Transgender", "Transgenderist", and "Transgendered" appeared in the proceedings of two New England Conferences on Sex and Gender in 1974 and 1975.
Virginia Prince Misconception
There is a commonly-held misconception that the term Transgender/ed/ist was coined by Virginia Prince. The term did not appear in Dr. Prince's writings until the early 1980s. While it is very likely that this term did have multiple independent origins, it is highly unlikely that one of these early independent sources was Virginia Prince. The term was in fairly common usage at the Fantasia Fair 1977 and 1978 events, both of which had Virginia Prince as an attendee, so she was certainly exposed to the term in those years, prior to her usage in the written word.
The original usage of the term within the TG Community in the mid and late 1970s was twofold, but with significant variation. It was used as a "gap filler" as a label of self-identity between Transvestite and Transsexual, particularly for those who saw their orientation more in the gender-identity realm than in the dressing realm. It was also used in the context of an "umbrella" term, encompassing those who identified as transvestites, crossdressers, transsexuals, etc.
Here and now in the mid 2000-teens, the term is well-established as the "T" in LGBT and similar acronyms.
The term is also well-established as the overall inclusive term for the community of those associated.
The term "transgendered", as an adjective, has fallen out of favor, with "transgender" becoming the preferred adjective.