Definitions for "Thin section"
A slice of rock mounted on a glass slide and ground to a thickness of about 0.03 mm, thin enough for light to pass through many kinds of minerals.
A thin translucent slice of a substance mounted on a glass microscope beneath a cover slip. The substance can be a rock, mineral, bone, concrete, etc.
A 3/100-mm-thick slice of rock that can be examined with a petrographic microscope.