In literal terms trans is a Latin prefix meaning “across or beyond.”
If someone is transgender it means that their gender is not the same as the sex they were assigned at birth. Gender and sex are very different, see ‘What’s the difference between Sex and Gender?’ if you are unclear on this.
You can be born into a female body but have the brain of a man, or the other way around. That disconnect between your brain and your body is what it means to be transgender. It gets a lot more complex than that of course, as being transgender is on a spectrum, it’s possible not to identify with either gender (gender neutral) or through to being the most muscle bound type male, but still be proud of your female sexual organs.
Basically every transgender person is unique and they get to define what being transgender means to them. Don’t make the assumption that all transgender people want or believe in the same things, or that they think the same or are even the same politically. It’s just not the case, which is exactly like every other human on the planet.
Some things are conflated with being transgender but are not related directly. So what isn’t transgender? This is a gray area, but in general: Transvestites are not transgender, drag is not related to being transgender, cross dressers are also not transgender. Those are mostly optional part time activities for those that take part in them.
In short then; when you’re transgender it means your gender does not necessarily match the sex you were assigned at birth.
The Basics is a series of articles that form a short guide to transgender terms, trans history, and what it means to be trans. It’s not meant to be exhaustive but rather an easy place to get started. You can find all the Basics articles over here.