It's service

The O-2 visa is a non-immigrant classification for individuals who accompany and provide essential support to an O-1 visa beneficiary. The O-2 beneficiary must be coming to the United States solely to assist the O-1 principal in a specific event or performance and must possess critical skills and experience that are essential to the successful performance of the O-1 beneficiary. The O-2 classification generally applies to support personnel for O-1 beneficiaries in the fields of arts, athletics, motion pictures, or television.
 
Carnegie Evaluations assist O-2 petitioners by facilitating a customized expert opinions from qualified subject-matter experts. After reviewing the relevant documentary evidence, the expert can provide an independent analysis of the beneficiary’s specialized skills and experience and explain why those skills are essential to supporting the O-1 beneficiary and cannot readily be performed by an ordinary worker.