It means it's a thin layer of veneer. Veneer is real wood that is often around 1mm thick. The most common usage is for doors and cabinet frames. The core consists of MDF, which is compressed wood pulp with a brown color. If the wear layer is 1mm, it is not recommended. Additionally, the boards are often unedged, meaning you can see the MDF core around the edges. IKEA now uses 4mm veneer on particleboard for their oak boards. This at least provides a wear layer that doesn't break easily. Durability depends on the treatment applied.