An "entry" indicates the number of times you are allowed to enter the country with the visa.
Single - The visa will allow a traveler to enter the country one time
Double - The visa will allow the traveler to enter the country two times.
Triple - The visa will allow the traveler to enter the country three times.
Multiple - The visa will allow the traveler to enter the country, essentially, an unlimited number of times.
Please note: Not all countries offer all options. Some countries may only offer a single entry, some may only offer single or multiple entry, and others may only offer multiple entry visas.
It is important to consider the number of entries for a few reasons. Generally speaking, multiple entry visas are valid for a longer period of time. For instance, a single entry will generally only be valid to be used within a few months whereas a multiple entry visa will generally be valid for a year or longer. If you may travel to the country in the future, obtaining a multiple entry visa now may save you money in the long run.
It is also important to consider the details of your trip. If you travel from the U.S. to India for a week, then travel to Indonesia for a week, and then connect back through India on your way home, this may be considered entering India twice, even if only to catch a flight. If traveling to China, taking a day trip to Hong Kong is considered an "exit" from China and then a "re-entry" upon return.
The passport card is a credit-card size U.S. passport that, just like a passport book, is proof of U.S. citizenship and identity but can ONLY be used to re-enter the United States at land border crossings and sea ports-of-entry from:
The passport card cannot be used for international air travel.
Please note: Just like passport books, passport cards are valid for 10 years for applicants 16 and older and 5 years for applicants under 16.