What is Localhost and what it means

About

localhost is:

• a hostname (ip name) that points to the host running actually the process (hence local)
• and a reserved top-level domain

It's used by a programs to connect to a services running on the same host, generally in a development environment.

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IP

This name is set to a private ip known as 127.0.0.1

With nslookup

nslookup localhost

Name:    localhost
Addresses:  ::1
          127.0.0.1