A deputy is a legislator in many countries, particularly those with legislatures styled as a Chamber of Deputies or National Assembly.
The deputies of the 12th Imam ( AS) during this time being in the major occultation are the most learned pious scholars who are recognized as Maraaji' of Taqleed. This is the guidelines which came from the 12th Imam (AS) to all Muslims after the forth special deputy Ali Ibn Muhammad Al-Samari.
Wasa'il al-Shia, 27:131.
The Marja' of Taqleed is a general deputy of the Imam (AS) and not special deputy names by the Imam (AS) like the four deputies who were during the minor occultation. (1. Uthman Ibn Sa'eed 2. Muhammad Ibn Uthman 3. Husain Ibn Rooh 4. Ali Ibn Muhammad Al-Samari).