Many expats who work in the UK want their relatives to come and visit or stay with them. Families are able to stay together in the UK thanks to the Family visa programme. To apply for a "family of a settled person" visa, the length of the stay must be at least six months.
Family members can apply for a Basic Visiting visa if they want to travel to the UK for less than six months to see their relatives. For those who reside outside of the EEA and Switzerland, this visa is necessary. It can only be requested if the person the applicant is visiting is a British national, a resident of the UK, eligible for humanitarian protection, or has received asylum in the UK.

https://www.visaandmigration.com/family-visas.html