A prism has the same cross section all along its length !

A cross section is the shape you get when cutting straight across an object.

The cross section of this object is a triangle ...

.. it has the same cross section all along its length ...

... and so it's a triangular prism.

Try drawing a shape on a piece of paper (using straight lines!),
then imagine it extending up from the sheet of paper,
- that's a prism !

No Curves!

A prism is officially a polyhedron, which means all sides should be flat. No curved sides.

So the cross section will be a polygon (a straight-edged figure). For example, if the cross section was a circle then it would be a cylinder, not a prism.

These are all Prisms:

Square Prism:

Cross-Section:

Cube:

Cross-Section:

(yes, a cube is a prism, because it is a square
all along its length)
(Also see Rectangular Prisms
)

Triangular Prism:

Cross-Section:

Pentagonal Prism:

Cross-Section:

Regular and Irregular Prisms

All the previous examples are Regular Prisms, because the cross section is regular (in other words it is a shape with equal edge lengths)

Here is an example of an Irregular Prism:

Irregular Pentagonal Prism:

Cross-Section:

(It is "irregular" because the
Pentagon is not "regular"in shape)

Volume of a Prism

The Volume of a prism is simply the area of one end times the length of the prism

Volume = Area × Length

Example: What is the volume of a prism whose ends are 25 in^{2} and which is 12 in long: