This technique is used for frostings (such as buttercreams, meringues or whipped creams) that have enough body to cling to the spatula.
Apply a dab of frosting to the side of the cake. Without lifting the spatula, spread the frosting away from you in a smooth, even stroke, moving forward, around and down. The spatula should avoid touching the cake, or it will pick up and spread crumbs on the frosting. Scrape the spatula on the edge of the bowl between strokes to get rid of excess frosting and crumbs, which could make tracks and mar the finish of your final coat.