An "onsite interview" means that the interview will take place in person at the location where the job or opportunity is located, rather than conducting it remotely or online. Full definition
This rarely occurs until the company has reduced its number of applicants to six or eight or less and is trying to find the top three for a round of onsite interviews. (sciencemag.org)
The phone interview enables you to screen the applicant's skills, knowledge, experience, and salary expectations before you invest company employee time in onsite interviews. (thebalance.com)
Happily, even if you didn't get to attend this year, there's something here for you, too, including dozens of onsite interviews with top authors from BEA, and an entire virtual writers conference, all just clicks away... (writerswin.com)