a surface has geometric free-boundary in a barrier hypersurface if its boundary meets the barrier orthogonally, like a bubble on a bathtub. we extend brakke's weak notion of mean curvature flow to have a free-boundary condition, and using toy examples we show why this extension is necessary. contrary to the classical flow, for which the barrier is ``invisible,'' the weak flow allows for the surfaces to ``pop'' upon tangential contact with the barrier. when the initial surface is mean-convex, we generalize white's partial regularity and structure theory to the free-boundary setting. this is in part joint work with robert haslhofer, mohammad ivaki, and jonathan zhu.