Is There a Bus Factor?

Any piece of code that can only be touched by one person, you have a problem if that person disappears or goes on vacation or gets sick. What I prefer is so definitely anyone can edit any code but people still have just areas of specialty maybe because they've developed a feature. There are some places that practice radical. No one can own any code and everyone works in every part. But it seems to me like a healthy team is able to work in each other's code.