Sexual orientation refers to each person’s capacity for profound emotional, affectional and sexual attraction to, and intimate and sexual relations with, individuals of a different sex/gender or the same sex/ gender or more than one sex/gender. Basically there are three predominant sexual orientations: towards the same sex/gender (homosexuality), towards the opposite sex/gender (heterosexuality) or towards both sexes/genders (bisexuality). 

Source: Council of Europe, Committee on Legal Affairs and Human Rights (2010) Discrimination on the basis of sexual orientation and gender identity, p. 7.