What is meant by “research visit”? I am a Ph.D. student of computer science and just have started working on a research problem. Some fellow Ph.D. students have mentioned the term research visit. For a professor, these things make sense, but as a Ph.D. student I am not getting what it means. There are some precise questions related to this below:


What does research visit mean?
What is the significance of it in Ph.D.?
What is the typical duration of a research visit?
You can be referring to two things, a visit to another institution (usually to give an invited talk) or you could mean a visiting student/researcher role:


Someone who visits a different institution for some prolonged period of time, usually to do research. You may even be able to register for classes.
It gives you the opportunity to work onsite with a different research group. You can think of it like an internship. Working onsite has a lot of benefits over working with a group remotely, such as direct access to lab equipment, data, participants, and your collaborators. 
It can vary greatly, but I've seen it range from a summer to an entire year.


UC Berkeley has a page describing some benefits of visiting student researchers.