A Tafsir is an exegesis; a detailed explanation.
With relation to the Holy Quran, a Tafsir serves the function of contextualizing a particular verse thereby making it easy to understand the wisdom and message contained in a verse making them easily applicable to one’s life. For example, many verses cannot be easily understood, even when explained in simpler words (in Arabic), or when literally translated into another language. Therefore, a Tafsir will shed light on a verse through a historical context, breaking it down word for word and elucidating its contemporary applicability, to say the least.
Who is a Mufassir (writter of Tafsir)?
A Mufassir is a religious scholar of the Holy Quran and Sunnah, who through personal religious and academic life proves his worth and capability to undertake the task of doing a Tafsir of the Holy Quran Of the many qualifications required for such an undertaking, often times this is an act of goodwill, for the purpose of disseminating Islamic knowledge, and to show his servitude to Islam.
Who can make a Mufassir?
A person who is unqualified is not permitted to take upon the task of Tafsir because without the proper qualifications, an illegitimate Mufassir will give rise to fitna (mischief), discord, and misinterpretation of the message and teachings of the Holy Quran. For those wishing to advance their study of Islam, it is important to thoroughly vet a Mufassir before proceeding to read his Tafsir; the same is important when consulting a translation of the Holy Quran.