In this subtitle the following words have the meanings indicated. “Airport” means Baltimore–Washington International Thurgood Marshall Airport. “Annual day–night (average) sound level” means the annual average aircraft noise level occurring during a 24–hour period, the calculation of which includes the addition of a 10 decibel penalty to noises occurring between 10 p.m. and 7 a.m. daily. “Avigation easement” means a written privilege granted by a homeowner related to aircraft overflight, noise, and associated effects which may arise in the ordinary operation of the airport. “Board” means the Board of Airport Zoning Appeals established under Subtitle 5 of this title. “Cumulative noise exposure” means a calculated or measured value for the exposure to aircraft noise in a 24–hour period, using the annual day–night (average) sound level (LDN) methodology. “Homeowner” means an owner of residentially used real property situated within the airport noise zone. “Noise zone” means an area of land surrounding the airport within which the cumulative noise exposure is equal to or greater than the lowest limit for cumulative noise exposure established by the Executive Director, under Subtitle 8 of this title. “School” means a public or privately operated elementary, secondary, postsecondary, or noncollegiate institution, with facilities in use on or before April 1, 1987, which is: Located within the airport noise zone; and Certified or accredited by the State Board of Education.