American Board of Opticianry (ABO) Practice Test

DBL stands for "Distance between lenses", which refers to the horizontal distance between the two lenses of a pair of glasses. Option A, "Effective diameter", is incorrect because this refers to the lens diameter, not the distance between them. Option C, "Diopter baseline limit", is incorrect as it is not a commonly used term in opticianry. Option D, "Dual bifocal lens", is also incorrect because this term does not encompass the specific measurement of the distance between lenses.