Single entry visas are intended for travelers who are going to enter a country once and then leave to either continue their journey or head home.
The concept of a double entry visa is simply that a single visa will allow you to enter your destination country (the country that issued the visa) twice.
Most countries offer double entry visas for tourist, business, and transit visas.
Most visas are issued with a time frame. So if you are given 90 days, you will have to enter and leave the country twice before the 90 days are up.
A double entry visa will not be approved for more days than a single entry visa. All countries have a set amount of days for which they are willing to issue for a tourist visa; a double entry visa merely allows you to enter the country twice during that time period. This period will not be extended just to allow you time to leave and re-enter.
To avoid being stranded, make sure you know where you are going. Some places that you travel may use one of your exit passes on a double entry visa. This is a common problem when traveling within a commonwealth country or territories. For instance, there has been confusion with exiting mainland China and entering Hong Kong. Double-check with the embassy to be sure which places will or will not require you to use a pass on your visa.
