What is the beat definition of jobs in the hidden job market?

The hidden job market is any place where jobs get filled without being formally posted or advertised. Sometimes a job may be created around the skill set of a person -- perhaps the person has met with an employer and proposed a certain project, or perhaps the employer has had an idea and sought out the potential employee through their professional or personal networks. Sometimes a person may get referred to a job before it is even posted. Employers may chose to "put out the Word" that a job has become available amongst their staff, sometimes even offering a "signing bonus" to the referrer if their suitable applicant is hired. Often, a member of staff in a company is aware that a position is becoming available (perhaps they know that a colleague is pregnant or has decided to leave) and will suggest to a job searcher to submit their resume before the position has to be advertised. The data about how many jobs are never posted is not clear, and this has obviously changed a lot as the internet has become easier to use. What is clear is that the hidden job market is less competitive and less rigid, and it enables applicants to apply for positions for which they perhaps may not have qualified, had the posting been formally advertised.