The residence of third-country nationals in Portugal is defined by the motive of their entry and duration of their stay. For short-stays, the third-country nationals must respect the Schengen rules. For long-stays, for more than 3 months, they have to respect the current national legislation.
There are some exceptions that allow the entry and staying of third-country nationals in Portugal, with visa exemption.
SCHENGEN VISAS
A Schengen visa is a short-stay visa allowing its holder to circulate in the Schengen area, during the period of its validity.
Short-term stay visa
The Schengen short-stay visa has a maximum validity of 90 during any hundred and eighty (180) days period, allowing one or multiple entries.
Short-term visa for season work
Seasonal work visas are issued to allow anyone wishing to engage in subordinate seasonal work, for a period of over 90 days (and a maximum period of 270 days), in previously approved fields of work.
Airport Transit Visas
Airport Transit Visas are granted to allow a person to transit within the international area of an airport, from one flight to another, without entering the Schengen area.