An apostille refers to a certificate or ‘apostille stamp’ issued to verify the signatures presented on an official UK document.
It authenticates the signatures showing that they were issued by the appropriate regulatory office in the UK.
The apostille service provides an international certification comparable to notarisation in domestic law, and it usually supplements any local notarisation of a UK document.
It can be used on a UK birth certificate for intercountry adoption procedures and other UK documents required for foreign investment procedures or intellectual property rights abroad.
The apostille must be issued as per the Hague conventions, which specify the international treaty with a foreign state.
They can be used for international relocation when you need to authenticate your documents for use in a different country, and they are also used for international marriages. Additionally, an apostille may be required for death certificates.
The Hague Convention states that the apostille stamp is enough to authenticate the legalisation process, and no other procedures are required.
Further reading: What is an apostille?