Por que preciso adicionar um período após o nome do host para que a resolução de DNS funcione?

Question

C:\Users\david>nslookup home-pi3
Server:  UnKnown
Address:  192.168.1.1

Name:    home-pi3
Address:  192.168.1.81


C:\Users\david>ping home-pi3
Ping request could not find host home-pi3. Please check the name and try again.

C:\Users\david>ping home-pi3.

Pinging home-pi3 [192.168.1.81] with 32 bytes of data:
Reply from 192.168.1.81: bytes=32 time=100ms TTL=64
Reply from 192.168.1.81: bytes=32 time=4ms TTL=64