Et-Tafsīl is interpreted in two ways:
1. Et-Tafsīl is used in the sense of bayān (clear exposition) and to explain extensively; as in the following verses:
It is not a fabricated statement (.....) It is a detailed explanation of everything.
(that is, it is the bayān (clear exposition) / extensive explanation of everything), (Yūsuf/111)
We have written down everything; as an admonition and a detailed explanation (that is, for bayān / to explain extensively) of everything. (A'rāf/145)
Indeed, We brought them a Book which We have detailed with knowledge (that is, We have made its bayān / explained it extensively). (A'rāf/52)
A Book whose verses have been made firm and then detailed (that is, its lawful and unlawful have been made bayān / explained extensively). (Hūd/1)
A Book whose verses have been detailed (that is, its verses have been made bayān / explained extensively), an Arabic Qur'an (recitation). (Fussilat/3)
We have detailed everything in it / We have detailed it in every respect (that is, We have made its bayān / We have explained it extensively and as required). (Isrāʾ/12)
He is the One Who has sent down the Book to you in a mufassal (that is, made bayān / explained extensively) manner... (Anʿām/114)
2. Et-Tafsīl is also used in the sense of baynūna (separation, being distinct, to separate); as in the following verses:
Mufassal [separately] verses (that is, for there to be a month between each of the two punishments and for each to be a distinct miracle from the other)... (A'rāf/133)
When the caravan had separated (that is, when his companions departed from Egypt)... (Yūsuf/94)
The Day of Fasl (that is, the Day of Bayān [separation/distinction]—which is the Day when judgment will be passed among people: one group will go to Paradise, another to the blazing Fire)... (Mursalāt/13)
Indeed, the Day of Fasl (that is, judgment and separation) is an appointed time. (Nabaʾ/17)
Indeed, the Day of Fasl (that is, the day when the separating judgment will be given among people) is the appointed time for all of them. (Dukhān/40)