Modern - Comtemporary or Frameless Cabinets mean the same thing.

Simply put the cabinets have no frame and should be made out of MDF. A box made of plywood needs a frame (traditional boxes) because plywood left alone will warp.

What exactly is MDF: Medium density fiberboard or MDF, is a composite wood similar (but totally differant in the cabit is made out of wood waste fibers glued together with resin, heat, and pressure. MDF is appropriate for many applications, from cabinetry to moulding, because it is smooth, uniform, and won't warp. MDF is also resistant to humidity, (not completely) but will hold it's shape in high humidity places like a bathroom.

MDF has a bad reputation because most people think it's partical board. It is not. It is engineered to be very stable and as it is name DENSE.