A number that can't be simplified to remove a square root (or cube root etc).

Examples:

• √2 (square root of 2) can't be simplified further so it is a surd

• √4 (square root of 4) CAN be simplified to 2, so it is NOT a surd

Examples:

• √2 (square root of 2) can't be simplified further so it is a surd

• √4 (square root of 4) CAN be simplified to 2, so it is NOT a surd