The Vander Elst visa is a type of visa or work permit available to non-EEA/EFTA citizens employed by and working for a company in an EU/EEA/EFTA country, that allows them to work for that company in another EEA/EFTA member state, subject to meeting certain eligibility conditions.[1]
The name comes from a legal case where the Belgian entrepreneur Raymond Vander Elst appealed his case to the European Court of Justice and won in 1994.[2] He had won a contract in France, but got bureaucratic trouble with his Moroccan employees.
However, it seems to vary how this is implemented, and often non-EEA-citizens need a normal work visa or work permit when working in another member country regardless of employer[3]