In other words, THIS IS NOT A COMPREHENSIVE GUIDE, nor does this pretend to be as such. This is intended to be a starting point for future research into the orientations presented here, among others.
Common Sexual and Romantic Orientations
Sexual orientation refers to who you are attracted to, either physically and/or romantically. The "or" is important as physical and romantic attractions are not the same, and they sometimes exist independently of each other. As a result, sexual orientations are expressed in terms of both physical and romantic attractions, with the romantic attraction named first. For example, an aromantic homosexual is physically attracted to the same sex, but not romantically attracted to anyone.
Experiences sexual attraction. The opposite of "asexual", and a term used primarily within the asexual community. Often abbreviated as "allo".
Not physically attracted to anyone. At all. Can still be romantically attracted to other people, and are often physically capable of enjoying sex. Often abbreviated as "ace".
Physically attracted to either male and female people, two genders, or to people who are the same or other gender as themselves. Historically, bisexuality referred to attraction to both male and female since the term predates the awareness of non-binary identities, but bisexuality as a term has been expanded in recent years to "same and other" to be more inclusive of trans* people. This expansion has caused some clashes with the pansexual community, who feel that the expansion is a form of erasure.
Generally not physically attracted to anyone, however, can develop a physical attraction to someone they have a strong emotional bond with. Demisexual people are a type of gray-asexual; in other words, they relate to being asexual for most of their lives and generally experience no or very weak sexual attraction to other people.
Unlike asexual people, gray-asexual people are capable of occasionally experiencing physical attraction, sometimes regardless of emotional bonding. In contrast, demisexual people, which are a specific subset of gray-asexuality, require a strong emotional bond to experience physical attraction. Gray-asexual people may also specify which gender(s) they are romantically attracted to, i.e. panromantic gray-asexual.
Attracted to the opposite sex, i.e. male-female and female-male. Often considered to be the default orientation, as the majority of people are heterosexual. While technically this can be used to refer to anyone who is physically attracted to a sex/gender not their own, it is almost exclusively used in binary terms of male and female.
Attracted to the same sex. Traditionally, this has meant male-male and female-female; though it can also refer to other identities, it is almost never used in this manner.
Strictly speaking, omnisexual people are attracted to all people. Most omnisexual people include various gender identities within their sphere of attraction, in addition to a person's physical sex. However, not all omnisexual people recognize all identities, and so there is a lot of overlap with pansexuality.
Strictly speaking, pansexual people are attracted to all sexes. As a result, a lot of pansexual people limit their attraction to physical sex, such as male and female, and sometimes trans men, trans women, and intersex people. Other pansexual people include non-binary gender identities, such as genderqueer and transgender, within their sphere of attraction, and so there is a lot of overlap with omnisexuality.
Attracted to some, but not all, genders. Sometimes overlaps with pansexual.
Important Notes: Because of how gender and physical sex are often conflated, some of the terms used to describe physical attraction also include gender, which is not a physical trait. It's worth noting that some people do experience physical attraction to specific genders regardless of physical sex, and that romantic attraction to specific genders regardless of physical sex occurs as well.
Not romantically attracted to anyone. At all. Can still be physically attracted to other people, and are usually capable of forming strong emotional bonds with others (just not romantic ones).
Similar to bisexuality, can mean romantically attracted to either male and female people, two genders, or to people who are the same or other gender as themselves. Sometimes overlaps with panromanticism.
Generally not romantically attracted to anyone, however, can develop a romantic attraction to someone they already have a strong emotional bond with. Demiromantics are a type of gray-romantic, and generally don't experience strong romantic attraction
Gray-romantics are capable of experiencing romantic attraction, though it may be infrequent, and they may not desire a romantic relationship, or may desire a relationship that's somewhere between platonic and romantic. Gray-romantic people may also specify what genders/sexes they are attracted to, i.e. gray-heteromantic bisexual.
Attracted to the opposite gender, i.e. male-female and female-male. Often considered to be the default orientation. While technically this can be used to refer to anyone who is romantically attracted to a sex/gender not their own, it is almost exclusively used in binary terms of male and female.
Attracted to the same gender. Traditionally, this has meant male-male and female-female; though it can also refer to other identities, it is almost never used in this manner.
Attracted to all genders. Sometimes overlaps with biromanticism.
Attracted to more than one person simultaneously. Polyamorous people are not always involved in polygamous relationships.
Important Notes: There are a lot more romantic and sexual orientations than just the ones mentioned here. The ones mentioned here are only the most widely-recognized.