Shodor Education Foundation
Shodor Interactivate: Lesson: Lines, Rays, Line Segments, & Planes
This robust lesson plan for upper elementary and middle school grades introduces the concepts for lines, rays, line segments, and planes. Resources are linked to it and ready for your use.
The Math League
The Math League: Basic Terms: Endpoints
This tutorial features an explanation of endpoints.
The Math League
The Math League: Basic Terms: Parallel Lines
This tutorial provides an explanation and example of parallel lines.
The Math League
The Math League: Rays
This website gives a very brief explanation and example of rays.