Relief at source is a method of tax relief that is used in the United Kingdom to reduce the amount of tax that is deducted from an individual's income. It is typically used to claim tax relief on pension contributions, and it allows an individual to receive tax relief on their contributions at the same time that they are made, rather than having to claim the relief on their tax return at a later date.

Under the relief at source system, the pension provider is responsible for calculating and applying the tax relief to the individual's contributions. The individual's gross contribution (the amount before tax relief is applied) is paid to the pension provider, and the provider then claims the tax relief on the individual's behalf and applies it to the contribution.

Relief at source is intended to make it easier for individuals to claim tax relief on their pension contributions and to ensure that they receive the full amount of tax relief to which they are entitled. If you have any questions about relief at source or need help with your pension contributions, you may want to consult with a financial or tax professional.