Much of the discussion of transgender identities on this guide are concerned with binary trans people: those who transition from female to male, or male to female. But there are also people who identify outside of that binary.
Medical News Today has a good list of gender identities, with explanations for many genders that fall outside the binary. Some of the most common are as follows:
Nonbinary is an umbrella term for most people (but not all!) who don't identify as either male or female. Genderqueer is another word that has been used in a similar fashion.
Agender people do not identify with any gender and do not have a gender at all.
Genderfluid people tend to be flexible about their gender identity, and their gender expression may fluctuate in day to day life or over time.
Dictionary definitions of these terms are also available on the "Transgender and Beyond" page.