What is the meaning of the term 'Maktubat'?

Written collections of letters.

The correct answer is Option (4) → Written collections of letters.

Maktubat (literally, “written” collections of letters); letters written by sufi masters, addressed to their disciples and associates – While these tell us about the shaikh’s experience of religious truth that he wanted to share with others, they also reflect the life conditions of the recipients and are responses to their aspirations and difficulties, both spiritual and mundane. The letters, known as Maktubat-i Imam Rabbani, of the noted seventeenth-century Naqshbandi Shaikh Ahmad Sirhindi (d.1624), whose ideology is often contrasted with the liberal and non-sectarian views of Akbar, are amongst those most frequently discussed by scholars.