Cis gender refers to someone who was correctly assigned male or female at birth, versus someone who was incorrectly assigned a gender at birth and transitioned to their true gender. It’s important to those members of the Trans community, and there are problems that people who have transitioned deal with that others don’t.
For most of our Western history people have been socialised that there are only two genders; cis male and cis female and anyone who has defied these identities have been labeled with derogative terms. Because the ‘Gay scene’ has had drag queens (female and male impersonators), there have been many assumptions and stereotypes that any person with a gender outside of cis male and cis female is gay. In reality, a person’s sexual orientation is separate to their gender identity. Cis males who are feminine and cis females who are masculine, often find themselves branded as homosexual.
When we think of gender, people are socialised to combine a person’s genitalia with the gender brain which consists of psychological sex differences that reflect the interaction of genes, hormones and social learning on brain development throughout the lifespan. We see this in everyday life through diversities from masculine to feminine, in both males and females. Non binary could be viewed as the centrepiece of this diversity of cis female through to cis male and feminine through to masculine. Biologically; ‘gender diversity’, ‘personality traits’ and ‘behaviours’ exists in all of us.