Define capital gains tax (CGT).

Capital Gains Tax (CGT) is specifically a tax on the profit made from the sale of assets that have increased in value over time. This typically applies to investments such as stocks, real estate, or any other property that was sold for more than its purchase price. When an asset is sold for more than what it was originally bought for, the difference in value is considered a capital gain and is subject to taxation under CGT.

The reason this answer is accurate is that it directly addresses the core principle of CGT, which focuses on the profit derived from the sale of an asset rather than a tax on the asset itself or other types of income.

In contrast, the other choices refer to different types of taxation. Income from employment is taxed under income tax laws and is not related to asset sales. Property rental income is likewise taxed separately under specific rental income regulations. Investment earnings can encompass various forms of income such as dividends or interest, which are also taxed independently from capital gains. Each of these scenarios involves different tax implications and doesn't align with the definition of capital gains tax.