The most common names for a butterfly valve that has the stem out of the center of the valve & sealing area in 2 ways: The stem is out of the center of the valve body and the stem is not in line with the sealing area.
The seat is in the valve body and usually replaceable. The seat can met metal or primary soft and secondary metal (to allow for fire safety)
Ratings are usually #150, 300 & 600
Body and disc material typically Carbon and Stainless Steel