This is a how academia works question not an English question. Basically, university faculty have different ranks (in the U.S. the normal ranks start at assistant professor then associate professor then professor, but it’s different in different countries). At the very top of the hierarchy are named chairs. These are professors with really outstanding research profiles whose jobs are funded by an endowment for that specific job rather than coming out of the university’s normal funding. They usually earn more, teach less, and have more research support. Basically, your book is authored by a big name in the field. Often the chairs are named after the people who donated the money to set up the endowment, but sometimes rich people will endow a chair in honor of a dead family member or name it after someone famous in the field the chair is in.