It is the "thickness" of the cable. The thicker it is, the more current it can handle without its temperature rising.

3 x 1.5

Ideal for larger household appliances such as dishwashers, low-power electric cookers, or lighting fixtures in large rooms.

Single-phase

The single-phase extension reel connects to a household or professional 230V AC supply. It is intended for low or medium power devices, such as lamps, computers, or tools. The operating current usually ranges between 10–16A. It is easy to use and transport, but cannot power high-power machines. It is recommended to use cables of suitable cross-section to avoid overheating.