Employment visas are provisions indicated on a passport for foreign workers who are approved to enter the United States and work for a set period of time. ... If the application is approved by the United States Department of State, an employer can then sponsor an employment visa.
The difference between visa and work permit is that visa is a document acquired by an individual to enter a specific country whereas work permit is an employment letter issued by an employer to the employee needed for entering the country.
A Work Visa allows you to legally work in a certain country for a specific period of time. Most countries require you to have a job offer from that country before you apply for a Work Visa. The Company which has given you the job offer also needs to sponsor your Visa.
What are the requirements for a European Work Visa ?