WHO ARE IMAMS?
Generally the word 'Imam' or 'Imaam' means for a leader. However, in Islamic aspect, the word "Imam" used for the various recognized religious scholars or authorities in the various field of Islamic sciences.
DIFFERENT FIELD OF IMAMS
1. Imams of Madhab - Founders of four schools of Jurisprudence
2. Imams of Hadith compilation - Scholars who compiled hadith books
3. Imams of Hadith sciences - Scholars who did analytical researches on the grade of hadith
4. Imams of Aqidah - Founders of schools of Islamic theology
5. Imams of Sufism - Founders of schools of Islamic spiritualism
6. Imams of Tafsir - Scholars who interpreted Holy Quran
7. Imams of History - Scholars who compiled the Islamic history
8. Other Imams - Scholars who are expert in other field Islamic sciences
All the above religious authorities are called as 'Imam' by Muslims.
Also only those Imaams who adhered the aqidah (theology) of Ahlus Sunnah al Ja'maah are called as Imam by Muslims.
On the other hand, whoever adhered the aqidah (theology) of other deviant sects are not called as Imam by Muslims. But the followers of those deviant sects called their leaders as Imaam themselves.