A prism is a portion of a transparent medium bounded by two plane faces inclined to each other at a certain angle.
The two planes face ABED and ACFD inclined to each other are called refracting faces of the prism.
The line AD along which the two refracting faces meet is called refracting edge of the prism.
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The face BCFE opposite to the refracting edge is called base of the prism.
The angle A at which the two refracting faces are inclined to each other is called angle of the prism.
A section ABC made by a plane at right angles to the refracting edge is called principal section of the prism.