Question

what do you mean by Assam Himalaya

Answer 1

Assam Himalaya is a traditional designation for the portion of the Himalaya range between the eastern border of Bhutan, on the west, and the Great Bend of the Tsangpo River, on the east. The highest peak of this range is Namcha Barwa.

Answer 2

assam is a state of india
and
Himalaya is the mountain
here it defines the part of the mountain himalaya that is with in the state assam
Hope it's clear to you