The SA102 is a form used as a supplementary page to the main SA100 form when filing a self-assessment tax return in the United Kingdom. The SA102 form is used to report specific income types such as employment, self-employment, and partnership income.

The SA102 is divided into different sections for each type of income. For example, the section for employment income is used to report salary, wages, and other taxable benefits received from an employer. In the self-employment section, an individual should report turnover, gross profit or loss from self-employed trade, profession or vocation. In the partnership section, an individual will report the profit or loss from partnership trade, profession or vocation.

It's important to note that if an individual has more than one type of income, they will need to complete multiple SA102 forms to report all of their income. Additionally, the form will also require you to report other incomes such as property rental income, foreign income and trusts, etc. If you have any questions about the SA102 form or need help with your self-assessment tax return, you may want to consult with an accountant or tax professional.