In headhunting or active search, recruiters specifically approach potential candidates who might be suitable for a particular position. This primarily exploits the potential of the passive applicant market: candidates are primarily approached who are not currently actively looking for a new job. 
Headhunting is often used to fill management positions or jobs with specific qualifications.
In contrast, permanent placement refers to the matching of companies and candidates who are actively looking for a new position or actively seeking a new professional challenge.