I'm asking for a friend but he recently found out that his wife has been married 10 times. On the marriage license she stated she had married 3 times. Is this fraud ?

Not unless she's still legally married to one or more of them.

It would depend on the laws of the state where they were married. Each state has their own laws on how truthful one has to be on a marriage license.

Assuming all the marriages were legally ended, it is unlikely that a criminal prosecution would ensue. It might, however, provide grounds for annulment.

If she was married 10 times, then she was married any number less than 10 too. Strictly speaking.

The question is really how much he cares about her lying. But you asked under Law, so never mind that part.

It would not be any fraud that any police would have interest. And it would not make the marriage invalid.

If there is a reason for a divorce, just file for divorce