Campus hiring is the policy of the company to recruit bright candidates from the reputed institutions in order to retain the best talents in their companies. This process is finalised by having the participations of the representative of the companies with the Institutes where the best performers are offered jobs and in such process, placement - officers or any authorised officer of the Institutions also participates in the process of selection of prospective candidates.
Off - campus interviews are somewhat different than the former one in the sense that that there would be larger gathering of the candidates in the job - mela where candidates are selected with proper screening such as conducting written tests of the candidates followed by number of oral interviews to assess the potentialities of the aspirants. Lastly, there would be a medical - test to select the physically fit aspirants. Needless to say, in such process the best James are selected in order to maintain the image of the company.
Yes, hiring is via through the college placement process and you need not apply directly to the company for being recruited.