Dhatu

धातु 

In संस्कृत, verbs are formed from Roots called  धातुः. There are THREE types of Roots called

• Roots with no object (अकर्मक)
• Roots with single object  (सकर्मक )
• Roots with dual objects (द्विकर्मक )

Roots are also classified into THREE classes called

• Parasmepada (परस्मै )
• Atmanepada  (आत्मने)
• Ubhayapda (उभय)

All Roots fall under conjugation (गण) depending on how they get modified during usage. There are TEN conjugations named 1st, 2nd etc to 10th conjugation.
In संस्कृतं, their names are based on the starting Root of the conjugation (aarmabha dhatu). Thus,
First conjugation is called Bhavadi Gana because भू  /  भव is the first Root in that group.  Here is a table with the conjugation names.

Conjugation Names

First Conjugation	भवादि गण
Second Conjugation	अदादि गण
Third Conjugation	हादि गण
Fourth Conjugation	दिवादि गण
Fifth Conjugation	स्वादि गण
Sixth Conjugation	तुदादि गण
Seventh Conjugation	तनादि गण
Eighth Conjugation	रुधादि गण
Ninth Conjugation	क्रचादि गण
Tenth Conjugation	चुरादि गण