The phrase "quick whisk" means to mix or beat something rapidly using a tool called a whisk, which has a handle and several wire loops. Full definition
Fold the wet ingredients into the flour mixture using a large wooden spoon or rubber spatula, then give the batter a quick whisk to ensure everything is well mixed. (justsotasty.com)
You can sift them if you prefer but a quick whisk to blend does the trick. (strawberriesforsupper.com)
Remove your mixture from the oven and give it a quick whisk - if your batter seems thicker than the consistency of double cream then pour in a little of your reserved milk mix until the texture is right. (greensofthestoneage.com)