Umbrella terms are broad, usually not very specific terms that can be used to cover a large amount of smaller, more specific terms. In the LGBTQ+ community, umbrella terms have been used a lot to make talking about the community and different parts of it more simplistic.

Now, there are a bunch of umbrella terms within the LGBTQ+ community, so I'll go over the most common ones and explain what they mean.

- Queer! Queer is a word that has been used as a slur against LGBTQ+ people. Now, the slur has been reclaimed by many members of the community. Nowadays, queer is an umbrella term that includes all members of the LGBTQ+ community, so basically, anyone who is not cisgender or heterosexual can be considered queer. However, not all members of the community are okay with being called queer, so if you're unsure, you can ask people if they're fine with the term. Some members of the community also choose to describe their sexuality/gender as queer.

- Allosexual. Allosexual is a term that refers to anyone who isn't on the asexual spectrum. So basically, if a person feels sexual attraction, they can be considered allosexual.

- Transgender is an umbrella term that refers to all gender identities other than cisgender. This means that all people whose gender identity does not match the sex they were assigned at birth can be considered transgender.

- Nonbinary! It's a fairly broad umbrella term which refers to all people who are not within the gender binary. This includes, for example, genderfluid, agender, and bigender. Note that nonbinary can also be an identity by itself. As an identity, Nonbinary generally means being outside of the male/female gender binary.

- Bisexual. Even though the word bisexual usually refers to the sexual orientation, it is also an umbrella term. As an umbrella term, bisexual includes several other sexualities, such as pansexual and polysexual. Basically, a person who is sexually attracted to more than just one gender is a part of the bisexual umbrella. And being attracted to only one gender means being monosexual.

- Biromantic is used in a similar way to bisexual, except it is used for romantic attraction. So anyone who is romantically attracted to more than one gender can be considered biromantic.

- Alloromantic. Alloromantic is the same as allosexual, but for romantic attraction. So a person who feels romantic attraction can be considered alloromantic.

Some people within the community use umbrella terms as a way to define their sexuality/gender, while others use different, more specific terms. Some people choose to not use labels at all, and all of these are completely valid and okay ways to define sexuality, romantic attraction, and gender.

Sources:

https://www.minus18.org.au/articles/what-does-%22queer%22-mean-anyway
https://www.healthline.com/health/allosexual#What-does-it-mean?
https://www.verywellmind.com/what-does-it-mean-to-be-non-binary-or-have-non-binary-gender-4172702