The term 'plane surface' refers to a FLAT, two-dimensional surface. The crossword solutions for this term are TARMAC (6 letters), AREA (4 letters), FLAT (4 letters), and FACET (5 letters). TARMAC is a type of material used to construct roads and runways, which is usually composed of asphalt or concrete. An AREA is a two-dimensional space, such as a FLAT surface. FLAT is a synonym for plane, meaning having no curves or angles. Finally, a FACET is a FLAT surface on a three-dimensional object, such as a gemstone.