Onsite Bookkeeping is where a bookkeeper comes and works in of your office. This is very similar to having an employee working from your office where they use your office equipment and have access to all of the required information they need.
In the case of onsite bookkeeping, the person hired to do the bookkeeping will be physically present at the place of business where they have been hired. This is a great way for the bookkeeper to interact with clients one-on-one and gain personal insight on the business they are accounting for.