P60 is a document you need to get your overpaid taxes back. You might also need a P60 to file a tax return in your home country (in case you are from outside of the UK).
P60 is a summary of your income and all deductions from your income (including taxes, social payments etc.). Every UK employer has to issue P60's after the end of each fiscal year. Fiscal year in the UK is different from most of the Europian countries as it starts on 6th of April and finishes on 5th of April of the following year. Employers start sending P60's after 5th of April and they are obliged to send them to all employees by 31st of May. Often this schedule causes problems for foreigners in case they have to file tax returns in their home countries. For example a Czech (but also Slovak, Bulgarian, Polish etc.) citizen who worked in the UK should declare his foreign income in one's home country, but the Czech fiscal year starts on 1st of January and finishes on 31st of December. The tax return has to be filed by the end of March. Czech Tax office (but also Slovak, Bulgarian, Romanian etc) typically requires a P60 as a proof of foreign income but it gets difficult if an emoployer sends the required P60 in April (especially if the employee still works for the same employer). Tax offices might accept payslips instead of P60 but it is always their decision. The good news is that foreign income is not taxed in most countries due to double taxation agreements. For example a Czech/Slovak person who worked in UK has to declare the income but does not pay additional taxes or social and health insurance.Dendax now offers also package deals for people who worked abroad to get their local tax returns filed for a lower price or even for free. You can register here: https://dendax.com/cs/registrace/usa-danova-registrace