AVP is a very common title in the corporate world. Many banks use the title for customer-facing type roles, as it sounds better than "branch manager" or "business banker". Corporate titles are largely misunderstood, because they really don't mean very much outside of the executive positions. The fact is, titles like AVP cost companies zero dollars and gives employees a sense of worth and customers a sense of confidence in the them.
You mean for the government? Like Vice President Joe Biden? He has assistants but they would not replace him if something happened. The next person in line is the Speaker of the House. The current Speaker of the House is Nancy Pelosi, but in January she will be replaced by John A Boehner