What is Footprinting

Footprinting is the blueprinting of the security profile of an organization undertaken in methodological manner.
The information unveil at various network level can include details of domain name, network blocks, network services and applications, system architecture, intrusion detection systems, specific IP address, access control mechanisms and related lists, phone numbers, contract addresses, authentication mechanisms and system enumeration. 
Information gathering activity can be broadly divided into seven phases: 

1. Unearth initial information
2. Locate network information
3. Ascertain active machine
4. Discover open ports /access ports
5. Detect operating system
6. Uncover services on ports
7. Map the networks

Footprinting includes the first two phases listed above. Footprinting is required to ensure that isolated information repositories that are critical are not overlook or left undiscovered.