Transgender is a collective term that refers to persons whose gender behavior or gender identity (the internal sense of being female or male) doesn't conform to the sex they were assigned at birth. “Trans” is often used as shorthand for transgender.
Transgender individuals express their identities in different forms. For instance, some can use their behavior, attire, and mannerisms to portray the gender that best suits them.
Others choose to have surgery and use hormones to change their appearance. Doing this helps match their body to their gender identity.
There is also a group that doesn't classify gender as being either 'female' or 'male'. Instead, they identify themselves as genderqueer, transgender, or genderfluid.
Transgender people have diverse sexual orientations and gender expressions (who you are attracted to). Therefore, a transgender person can be straight, lesbian, bisexual, or gay.
Being transgender isn't like being bisexual, gay, or lesbian. Who you feel on the inside — whether female, male, none, or both — is what constitutes being transgender. Who you feel drawn to sexually or emotionally describes being bisexual, gay, or lesbian.