Short answers, pulled from the story.
A Subahdar was the governor of a Subah, meaning a province, in the Mughal Empire. The title comes from the Persian language and the official was also known as Sahib-i-Subah or Nazim. The Subahdar headed provincial administration and was assisted by a range of officials including the Diwan, Bakhshi, Faujdar, and Kotwal.
Subahdars were normally appointed from among Mughal princes or officers holding the highest mansabs, which were the top ranks in the Mughal system of military and civil grading. Appointing princes tied distant provinces directly to the imperial family.
The word Subahdar is of Persian origin. It designated the governor of a Subah, the Mughal term for a province.
The title was used under the Khalji dynasty of Bengal, the Mamluk dynasty, the Khalji dynasty, and the Tughlaq dynasty before becoming prominent in the Mughal era.
The Subahdar was assisted by the provincial Diwan for revenue, the Bakhshi for military affairs, the Faujdar for district troops, the Kotwal for urban policing, the Qazi and Sadr for justice and religious matters, the Waqa-i-Navis as a court news-writer, and the Qanungo and Patwari for land records.
Subahdar, Sahib-i-Subah, and Nazim were alternate designations for the same office: the governor of a province. All three titles referred to the head of Mughal provincial administration.