Question

why 10th class exams are named as boards what is meant by board

Answer 1

It is conducted by a board comprising members responsible for conducting exam.
The central board conducting exam is called CBSE.

Answer 2

Board exams are known that way because they are conducted by a board of members or a group who come together and select a few questions and conduct examinations. For CBSE schools it is the central board of secondary education which is in Delhi.