An abasic site, also known as an AP (apurinic/apyrimidinic) site or an AP site, is a location within a DNA molecule where one of the nucleotide bases has been removed or is missing. These sites can occur naturally due to spontaneous hydrolysis or can be induced by DNA-damaging agents. Abasic sites are significant because they can lead to mutations or DNA strand breaks if left unrepaired, and they are targets for various repair mechanisms within the cell.