Cisgender is a term for someone whose gender identity aligns with what they were assigned at birth.
The term is used to refer to “non-transgender” people without alienating transgender, agender, or non-binary people. It is often see as the ‘default’ identity, as the majority of children are assigned a male or female identity at birth. If, later on, a child agrees with the designation that was granted at birth, then they are cisgender.
While the term cissexual is sometimes used in correspondence to transsexual, it should not be confused with a sexual orientation. More often it is shortened to cis.