The U.S. Code of Federal Regulations (CFR) defines a basement as "any area of the building having its floor subgrade (below ground level) on all sides." In FEMA-designated floodplains in Maryland, the building of basement floors that are below grade on all sides is prohibited and "the bottom of the lowest horizontal structural member that supports the lowest floor shall be located at or above the flood protection elevation."
When converting basement space into habitable living space it must have at least two exits, one of which must be a door. One exit may be a window, but it must be a minimum of 24 inches high and 20 inches wide. The habitable room must have a minimum head space of 7.5 feet and be a minimum of seven feet by 10 feet. Bathrooms in the basement must vent to the outside. In addition to these standards, check with the city you live in for additional local code requirements.
Your city in Maryland will probably require you obtain a building permit to convert or finish a basement. However, you will not be required to submit professional, detailed plans of the intended conversion, if you are not going to do anything to the foundation, load-bearing posts or walls.