Footprinting is a term not exclusive to computer science, but often used in information technology to refer to efforts to find out about computer systems and their networks, or footprints. Although footprinting can be done for legitimate purposes, the term is often linked to hacking and cyber attacks.
When it comes to hacking, the term footprinting is used to refer to some of the work that hackers do quietly, behind the scenes, before they attack a system. This may involve looking at what operating system a hardware setup uses, or pinging the system to determine design properties. Port scanning or registry queries are also other types of footprinting. These types of information then build the plan for a cyber attack. In that sense, the word footprinting is used in information technology like the word casing is used for house burglary.
Regardless of its sometimes of sinister connotations, public tools exist for footprinting, including open source tools for Windows and Linux. These kinds of tools can enable scans of a system to look at URL handling, SSL certificates and other legitimate aspects of system security. These can be used to simply monitor a system, or to look for its weaknesses in terms of network security