Which is not a type of network?

UNIX is not a type of network.

UNIX is a computer Operating System which is capable of handling activities from multiple users at the same time.

There are several different types of computer networks. Computer networks can be characterized by their size as well as their purpose.

Some of the different networks based on size are:

• Personal area network, or PAN
• Local area network, or LAN
• Metropolitan area network, or MAN
• Wide area network, or WAN
• Some of the different networks based on their main purpose are:
• Enterprise private network, or EPN
• Virtual private network, or VPN

Hence option 4 is correct.

Additional Information 

Virtual Private Network:

• It is an encrypted connection over the Internet from a device to a network.
• It creates a private network to separate the user’s traffic from the rest of a public or shared network.
• The encrypted connection helps ensure that sensitive data is safely transmitted.
• A VPN extends a corporate network through encrypted connections made over the Internet. Because the traffic is encrypted between the device and the network, traffic remains private as it travels.
• A VPN hides your IP address by letting the network redirect it through a specially configured remote server run by a VPN host.

Personal area network (PAN):

A personal area network (PAN) is a network concerned with the exchange of information in the vicinity of a person. Typically, these systems are wireless and involve the transmission of data between devices such as smartphones, personal computers, tablet computers, etc. The purpose of such a network is usually to allow either transmission of data or information between such devices or to the server as the network that allows further uplink to the Internet. Developments in the area of Personal Area Networks (PANs) are largely overseen by the IEEE 802.15 working group