The plane. The surface of calm water (the sea, a lake, a pool, etc.), a table top and a piece of paper can be all examples of a plane, as long as we can imagine them extending indefinetely in all directions.
The point. A dot on a piece of paper made by a pencil or the small hole left by a needle prick are good examples of a point. A point has no dimensions. Also, points are usually designated with capital letters: A, B, C, ...
The straight line. A piece of string, the edge of a table or a ruler are good examples of a line. Lines are usually designated with lower case letters: r, s, t, ...
Segment. The section of a straight line between any two points A and B, is called a segment. A and B are the ends of the segment. It is called AB. The length of a segment is the distance between its ends. It is designated .
