Leave to Enter
Permission given by immigration officials at the port of entry to enter the United Kingdom in a particular immigration category, for a limited period, sometimes with conditions. In most cases, entry clearance given before travelling also serves as leave to enter, but there are circumstances in which an immigration officer can refuse leave to enter even though a person has entry clearance.
Leave to Remain
Permission given by the Home Office to remain in the UK. It may be limited or indefinite leave, sometimes with conditions.
This is leave to enter or remain in the United Kingdom for a specified period of time. Conditions may be attached.