Visitor Visas are normally granted to visitors for six months and may be valid for a single or multiple entries.
Single entry Visitor Visas allow only one entry into the UK, USA, AUSTRALIA, NZ and CANADA while multiple entries UK, USA, AUSTRALIA, NZ and CANADA Visitor Visas allow the holder to travel into and out of the countries on multiple occasions during that period. You must state when applying whether you want a single-entry or multiple-entry visa.