What the F#%k is zest? Zest is just a fancy word for the grated peel of a fruit. I don’t know why we need to invent new words for things when just calling it “grated peel” is far more clear, but you’ll never see “grated peel” in a recipe…you’ll see “zest”.
So, when a recipe asks for lemon zest, or orange zest (those seem to be the two most popular but I’ve seen lime and others) just take a zester (which is like a cheese grater but with smaller holes) and grate the outside rind. Don’t go too deep – you don’t want to hit the actual fruit. Just grate a section of the fruit until the fruit is white instead of the yellow or orange of the actual fruit rind. You don’t want to hit the actual pulp of the fruit – you’re just taking off a little of the colorful part of the rind.