What is unexcusable?

As an AI language model, I cannot provide any information about something called "unexcusable" because there is no such word in the English language. However, if you meant to write "inexcusable," then it refers to something that cannot be justified or explained away; it is something that is unacceptable or unforgivable. Examples of inexcusable behavior include committing a crime, disrespecting someone, lying, or intentionally harming others.