One of the important issues with visas is the number of entries allowed into the target country.
In general, we can differentiate between single-entry, two-entry and multiple-entry visas:
Single entry visa: This work visa will allow entry into the country only once. In case of exit, it will be necessary to reissue another visa to re-enter in a regularized manner.
Two-entry visa: similar to the single-entry work visa, with the difference that in this case we will be able to enter twice, as long as it is done within the period of validity of the visa.
Multiple-entry visa: allows unlimited entry into a country, and as in the case of the two-entry visa, they must be made within the period of validity.