Explanation
The ISREF function returns TRUE for a valid worksheet reference and FALSE is not.
INDIRECT then tries to evaluate the text as a reference.
When INDIRECT succeeds, the reference is passed into ISREF which returns TRUE.
When INDIRECT can’t create a reference, it throws a #REF error, and ISREF returns FALSE.
you might use the ISREF function to check for a reference in a formula.
INDIRECT Function
The Excel INDIRECT function returns a valid cell reference from a given text string.
INDIRECT is useful when you want to assemble a text value that can be used as a valid reference.
