Question

why virus are called bordered line between two living and non living?

Answer 1

Viruses have DNA and RNA, which are the characteristics of a living organism. But they do not have a protoplasm and are unable to exhibit life outside the host cells. The only times they are active is when they enter their host's cells. This is where they multiply, etc. 
They also display characteristics of both living and non living things, which is why they are termed as borderline organisms.

Answer 2

Viruses are active only when they are in the host cells. They reproduce only in hosts' cells and show no other life processes. Hence, they are considered on the borderline of living and nonliving organisms.