Demiromantic is a romantic orientation on the aromantic spectrum defined as someone who does not experience romantic attraction until they have formed a deep emotional connection with someone. The connection can be sexual, platonic, or some other form of connection. Forming an emotional bond with someone does not mean that one is automatically attracted to said person, as it just means there's now a possibility for one to feel attraction.
It is important to distinguish between typical romantic attraction to friends, sexual partners, and other people of close emotional bonds, and demiromanticism, which implies that there would be no romantic attraction to anyone unless a close relationship was to be established. The already existing relationship is the only way a demiromantic person would be able to experience romantic attraction. Being romantically attracted to one's close friends does not necessarily mean that one is demiromantic, for example.
Demiromantic can be a romantic orientation on its own or can combined with other orientations. An example of this would be of a person being demiromantic and gay (demihomoromantic), meaning that when one does experience romantic attraction it is towards people of the same or similar genders. Even though one may have a close connection to someone of a dissimilar gender, one may never feel romantic attraction to them.
The prefix demi- means "half" or "partial". The prefix is also used in words such as demigod.