Immigration is the process of entering the UK to stay, either for a short time or permanently.
A UK visa is a sticker placed in a passport at a UK visa office (outside the UK). The visa gives you permission to enter the UK (known as entry clearance). A visa will state the reason for your visit to the UK and how long you can stay.
An Entry Clearance Officer works at a UK visa office (outside the UK): he/she decides decides if a visa applicant qualifies for a UK visa.
An Immigration Officer works at an airport or other entry point in the UK: he/she decides decides if an arriving passenger qualifies for entry into the UK.
A visa national is a person who needs to obtain entry clearance before travelling to the UK.
A non-visa national is a person who does not require a visa for travel to the UK which is short-term (for 6 months or less).
If you are refused leave to enter, you are not given permission to come into the UK
Once you are in the UK you can apply for an extension of stay (to be able to remain longer in the UK), but not if you have a visitor visa.
A British embassy represents the UK in a foreign country (the ambassador is the most important person at the embassy).
A British consulate takes care of British people who are living abroad and supports British business.
A British High Commission represents the UK in a country which is part of the Commonwealth.
A UK diplomatic mission is a British embassy, High Commission or consulate. Many of these offer a visa service.
The Home Office is the government department which looks after the rights and laws of people living in the UK.
The UKBA (UK Border Agency) is the part of the Home Office which is responsible for immigration. Previously this was known as the IND (Immigration and Nationality Directorate) and as the BIA (Border and Immigration Agency).
The FCO (Foreign & Commonwealth Office) is the UK government department which is responsible for international relations.
The points-based system (PBS) is the name of the process currently being used for assessing applications for UK visas, divided into 5 sections known as tiers 1-5.
Tier 4 is the part of the points-based system which applies to students.