Definition
Side
A straight line segment forming one part of a polygon’s boundary.
What it means
Trace around a polygon. Each straight piece from one vertex to the next is one side. Counting those pieces tells you how many sides the polygon has, while measuring one piece gives that side’s length.
Remember it
A side is one straight fence piece around a polygon.
Example
A pentagon has five sides. If one side measures 4 cm, 4 cm is its side length, not the side itself.
Watch for
A circle’s curved boundary is not a polygon side, and a solid is described more precisely with faces and edges.
Common mix-up
A side is a geometric segment; side length is the number and unit that measure it.
Exact meaning
A side of a polygon is one line segment on its boundary, joining one vertex to the next. The side is the segment itself; its side length is the segment’s measured length.