If you've never heard of nutritional yeast before, you might be thinking of baking yeast, that stuff you throw in your bread dough to make it rise. Although both are forms of yeast fungi, nutritional yeast is different in that it's been heated up and deactivated. That leaves it a perfectly sprinkle-able, flaky consistency.
It also tastes very different. Baking yeast, if you haven't tried it, is gross. But nutritional yeast provides a sort of savory, umami-type layer to otherwise bland snacks, such as popcorn, pasta, or salads. Some describe it as "nutty," others say it's more "cheesy."
The biggest thing nutritional yeast has going for it, though, is that it's a complete protein, meaning it contains all nine amino acids. Most of us get complete proteins from meat. But other than eggs, there aren't many vegetarian foods that can provide that on their own. So nutritional yeast has become a go-to for vegans and vegetarians looking to add non-meat sources of protein to their diets. You certainly don't have to be vegan to give it a try, though.
Some types of nutritional yeast give you other nutritional benefits, too. Depending on the exact brand you're using, you might get some vitamin B12, zinc, and folic acid. Of course, as Time explains, nutritional yeast can't be your only source for these things. Eating a varied diet made up of actual food is the best way to get everything you need. And although you might be tempted, try not to sprinkle it on every single meal (it is possible to have too much of those nutrients!). But think of nutritional yeast as a seasoning treat — with a little extra protein punch.