It's a dietary supplement (B vitamin complex ) in the form of yeast flakes which are created by spray-drying liquid yeast and people use it for flavoring as well as adding flakiness to things, such as in keto baking (crackers, etc.). It has a sort of tang/umami flavor.

Vegans use it for B vitamins they can't get from their diet, and they shake it on foods as an alternative to shaker Parmesan cheese, too.

As with many dietary supplements, don't use too much of it unless you want the runs/upset stomach.