A centralized electronic system used to track and record transactions related to the trading of emission allowances under the EU ETS.

The trading unit is the carbon allowance, which represents the right to draw 1 ton of carbon from a capped carbon budget. In compliance markets, a regulatory entity fixes a certain amount (the cap) of allowed emissions for the year (the budget), and industrial polluters need to purchase allowances equivalent to their emissions. There are only as many allowances as the budget allows: the supply is capped. It is a regulated market in the sense that buyers have an obligation to hold allowances in equivalence to their emissions. Allowances are standard units issued by the regulatory body.

Facilities used for storing natural gas to balance supply and demand, ensuring energy security and stability of gas prices. The gas storage levels indicate whether there is more demand or supply in gas markets, thus influencing the price levels.