Not everybody who is visiting friends or family or even going on a short holiday may need a visa, it depends on your country of origin. Visits may also be for business, for marriage, for studies or for medical treatment.
These are the most common; these visas are valid for a maximum of 6 months. General visitors must not work when they are in the UK and must have their own finances to support themselves throughout the entire duration of their visit. The Standard Visit Visa has replaced the following Visitor Visas:
These visitors are people who are visiting the UK to have their ceremony but do not intend to live in the UK afterwards. These are given for a maximum of 6 months. However, if you do wish to live in the UK after your marriage, you will not qualify for this category so you must refer to the information on family relationships. All applicants need to obtain entry clearance to come to the UK in this capacity -even if their country of origin is not subject to a visa regime.
The maximum a student visitor can stay for is 6 months as long as they are 18 or over and have been accepted for an approved course of study, intend to leave the UK at the end of their stated visit, do not intend to engage in business or to study at a maintained school and can be maintained and accommodated without recourse to public funds.