BANGALORE, INDIA: Networks can be private, such as within a company, and others which might be open to public access.

Network security is an area in the field of networking. It encompasses protecting a network from outside intrusion and also define access for insiders (who are within a network).
 
As a starting step to security there need to be a policies, usually  developed by an administrator, to define who has access and to what within a network. These policies may define authorisations for access, privileges, prevention of access to particular sensitive folders/files or any other end-points on the network.
Often an IT administrator draws a line between insiders and outsiders for providing access on his network. The permissions from access may vary depending on role of an individual on the network.

According to Wikipedia, network security is generally taken as providing protection at the boundaries of an organisation by keeping out intruders (hackers). Network security is often mixed-up with Information security which explicitly focuses on protecting data resources from malware attack or simple mistakes by people within an organisation by use of data loss prevention (DLP) techniques. One of these techniques is to compartmentalize large networks with internal boundaries.