Many people are able to define the acronym LGBT, but give up once it has been expanded to LGBTQIAP. Each letter in the acronym is equally valid and important, yet a lack of education often leads to ignorance around the rest of the identities that encompass the LGBTQ+ community. A lack of understanding can also lead to miscommunication among fellow members of the community and allies. For example, some (usually straight) people claim that the A in LGBTQIAP means "ally", but it doesn't. Although allies are an important part of our safety and awareness, they simply cannot be included in our acronym. Leaving out allies is not a matter of exclusion, but to avoid erasure of the entire purpose behind the acronym. If allies could be included in the LGBTQ+ acronym, then there would be no purpose behind having a distinguishing acronym in the first place. We embrace the differences that our identities provide us, but want to keep non-LGBTQ+ people separate from those who form our community. Asexual is one of the identities that a person in the LGBTQ+ community may choose to label themselves as. Asexual people sometimes refer to themselves as "aces" for short. Asexuality is an umbrella term, much like transgender can be one as well. Asexual means a lack of sexual attraction. People who identify as asexual may experience other types of attraction like romantic or platonic, but not sexual. Aromantic is another term that is represented by the 'A' in the acronym. Aromantic means a lack of romantic attraction. Of course, these terms may have differences in their specific meanings from person to person. Some aces may experience a little sexual attraction or none at all, while aros (aromantics) may experience very little to no romantic attraction. Further under the asexual umbrella are demisexuals, which are people who require a strong emotional bond before experiencing sexual attraction.
Human sexuality is a spectrum, just like gender identity. A graysexual person may identify somewhere in the 'gray area' between sexual and asexual.
As humans, our attitudes/behaviors/beliefs/identities are fluid and maintain the possibility of change. If somebody identifies as asexual at one point, they can always later change that identity. Not to say that these people will change or are just "confused" or "undecided". All people under the asexual umbrella are valid, and if they decide to change their label, they are still valid.
For more information regarding asexuality or how to be a better ally: https://www.thetrevorproject.org/trvr_support_center/asexual/