The correct answer is option 'C', World Trade Organisation (WTO).

Explanation:
- The World Trade Organisation (WTO) is an international organization that deals with the global rules of trade between nations.
- One of the main functions of the WTO is to regulate and monitor the use of subsidies by member countries.
- Subsidies are financial assistance provided by governments to domestic industries, which can distort international trade.
- The WTO has defined different types of subsidies, including the Amber box and Green box subsidies.

Amber box subsidies:
- Amber box subsidies are considered to be trade-distorting subsidies that have the potential to negatively impact international trade.
- These subsidies are subject to reduction commitments by member countries.
- They include subsidies that are directly linked to production quantities, prices, or exports.
- Amber box subsidies are considered to be the most trade-distorting and are subject to the most stringent regulations and reduction commitments.

Green box subsidies:
- Green box subsidies are considered to be non-trade-distorting subsidies that have minimal impact on international trade.
- These subsidies are not subject to reduction commitments and are allowed without any limitations.
- They include subsidies that are deemed to be government payments that do not distort trade, such as those for research, environmental protection, or infrastructure development.

Significance of Amber box and Green box subsidies:
- The distinction between Amber box and Green box subsidies is significant because it determines the extent to which a subsidy is permitted under WTO rules.
- The WTO's Agreement on Subsidies and Countervailing Measures (ASCM) provides guidelines and rules regarding the use of subsidies by member countries.
- The ASCM sets out the criteria for classifying subsidies into different categories, including the Amber box and Green box.
- The classification of a subsidy determines whether it is subject to reduction commitments or allowed without any limitations.

In conclusion, the World Trade Organisation (WTO) has defined the terms Amber box and Green box for subsidies. These classifications are important in determining the extent to which a subsidy is permitted under WTO rules and regulations.