This is an important distinction.
Single Entry
You enter Vietnam once.
If you leave the territory, the visa usually does not allow for re-entry.
Multiple Entries
You can exit and then return during the validity period of the visa.
This is particularly useful if you are temporarily living in Vietnam and wish to travel to, for example:
- Thailand;
- Cambodia;
- Singapore;
- Malaysia;
- Japan;
- South Korea.
For a period of several months, the multiple entry option can therefore be much more convenient.