Calories - the basic unit used to measure dietary energy. The unit used for nutrition (as opposed to Calories used in physics) are actually kilo-Calories, but they’re usually just called calories. Excess calories will be converted and stored as fat.

Glucose - a simple sugar monosaccharide (just 1 sugar component). There are other basic, simple sugars like galactose, and fructose. Combining two of these simple sugars yields a disaccharide, which is a complex sugar as it requires breaking down into its constituent sugars before it can be digested and absorbed. For example, ordinary table sugar is sucrose (glucose and fructose), but the sugar you find in fruits is just plain old fructose. Sugars, both simple and complex, are carbohydrates. Simple sugars/carbs are quickly digested and absorbed into the blood stream.

Complex carbohydrates - these are long strings of complex sugars (polysaccharides), such as starch. As a result, they are very calorie dense. Since they are strings of complex sugars, they require even more breaking down before they can be digested than regular disaccharides. They require time to digest fully.

Gluten - a structural protein formed mainly of the naturally-occurring glutenin and gliaden proteins found in some grains. If you add water and knead wheat flour, like in bread dough, it will form a network of these proteins into gluten. This is what gives bread its elasticity. Around 80% of all the protein in bread is gluten. Because it’s sort of a dietary buzzword, I’ll add that it’s typically perfectly safe to consume unless you’ve been directed by a doctor to avoid it; avoiding it will produce no health benefits at all for the vast majority of people. There is some debate on whether gluten sensitivity truly exists outside of celiac disease (which is autoimmune in nature). Triple-blind experiments where subjects who claimed sensitivity were given high-gluten diets and reported no more symptoms on average than those given low-gluten or gluten-free diets. It’s possible that the true cause of intestinal discomfort for some is instead from a group of compounds called FODMAPs, which are also present in many gluten-containing grains. Follow-up experiments with diets high in FODMAPs with the same group yielded more reporting of symptoms than with the gluten.