Three Month Multiple Entry Visa means the visa is valid in three months and you can go in and out Vietnam as any times as you wish within three months...
Arrival visa means the visa that you can collect upon arrival at the airport. The advantages of arrival visa is you will not need to go anywhere to apply for the visa and it is convenient for people who really want to save their valuable time in business....
Only citizens of certain countries can visit Vietnam without an entry visa (valid for visit within 30 days). Those countries include: Thailand, Philippine, Malaysia, Singapore, Indonesia, Laos, Korea, Japan & Scandinavians (2005)....
What is a 'Visa on Arrival ? This is most likely the easiest way to obtain your visa without having to chase down embassies, consulates and the like prior to your trip, and is a valid alternative when applying for a tourist visa....