Malt is a generic term for a sweet and strongly flavored product of fermentation. In the USA the term malt may, and usually does, refer to barley malt. Since barley is one of the three grains that celiacs must avoid, malt should be considered highly suspect as an ingredient.
Sometimes malt is made from grains other than barley, corn is one example. A malt flavoring made from corn should not be a problem for a celiac, unless they are unlucky enough to be also unable to eat corn.
The problem is, if the ingredients just say malt you have no way of knowing the source of that malt.
The safest and wisest thing to do is avoid foods that contain malt, unless you can contact the manufacturer and receive assurance that you trust that their malt is not made from barley.
Steve