Answer
A cryptogram is a message coded so that no one other than the intended recipient
can understand (decode) it.
Work Step by Step
A cryptogram is a message written so that no one other than the intended recipient
can understand it.
The procedure (see p.637):
1. Assign each letter a numerical value, (A=1, B=2, ... Z=26, space=0)
2. Convert the numerical values of the message into a matrix.
3. Multiply with an inveritble matrix to code the message.
4. The recipient must know the inverse of the matrix (chosen in step 3) to decode the message.
