Indefinite Leave To Remain (ILR), also known as Settlement, is the right to stay in the UK without any time restrictions.
You can apply if you meet the residence requirements of having lived in the country for five years. You can also apply as the spouse, partner or child (under 18) of a settled British citizen.
If you have been a member of HM Armed Forces (i.e Brigade of Gurkhas) for a minimum of four years, you are entitled to apply for ILR.
You may be barred from being granted indefinite leave to remain if you have a criminal record or are found to have previously made fraudulent applications for entry to the UK, or lied during an application.