what are these "macros" that everyone talks about?

macros are macronutrients. Carbohydrates, Protein, and Fats are macronutrients. Regarding going over or under - in my opinion it's fine to go over or under your macros as long as you are under your calorie goal. Many people here, including me, have certain macro goals they try to hit each day. Mine, for example, is 45% protein, 35% fat, and 20% net carbs. I have manually changed my macro settings here to reflect those goals.