Full Scope refers to a type of polygraph examination which someone might be asked to undergo as part of the investigation process before getting a security clearance. At one point, you could either get a counter-intelligence polygraph examination, where you were asked questions basically to determine if you were a foreign agent, or approached to work on behalf of a foreign agent, and that would take half a day, or you could be given a "full scope" polygraph examine, which might take a full day, and would ask a much larger invasive set of questions about your lifestyle. For example, a decade or two ago, you might be asked questions about your sexual practices and/or identity lest that be used as blackmail leverage by a foreign agent. (For example, if you say, were into golden showers, and were trying to keep that a secret, might Russia be able to use the threat of making a video tape of that practice to get you to betray your country?)

Access to some security comparments ("Sensitive Compartmented Information") might require both a need to know, and either a Counter-Intelligence or Full Scope polygraph examination. If you have a current (non-expired) TS/CI Poly or TS/FS Poly investigation, could be quite valuable to a defense contractor, because it can take a while (potentially months or years) and cost $$$ for you to get that investigation, which combined with the need to know, would be necessary to get you access to certain classified compartments which might be necessary for you to work on a particular project. Otherwise, you might have the necessary computer skills, but without having the requisite security clearance investigation having been done on you, the defense contractor might have to hire you and have you work on non-classified aspect of the projects for months and months (or if you are a new college grad, maybe even twiddling your fingers) until the security clearance investigation had been completed.