What is the difference between UHPLC and HPLC columns?

The main difference is the size of used particles filled into the column. Particle sizes ≤ 2 µm are commonly used for UHPLC. Particles with a size of 3 µm up to 5 µm are usual for classical analytical HPLC.
Furthermore the column inner diameter is varying. KNAUER UHPLC columns come with an inner diameter of 2 mm. Columns with an inner diameter 3 mm - 4,6 mm are analytical HPLC columns.