Scanning is part of the Reconnaissance phase where the attacker gathers information about a target. It is type of active reconnaissance during which the network and systems are scanned. In the scanning, the live systems (IP addresses) are found and then the active ports on a system are identified. Post which, OS type (Windows, Unix, Linux) and the list of services present on the system are gathered.
Types of Scanning
Ping sweep is scanning process of finding all the IP address in a subnet.
Port sweep is scanning process of finding all the ports on the system.