There is no formal definition for the expression “Boolean Strings.” Recruiters and Researchers use the term “Boolean Strings” as a shortcut to advanced Google search strings (i.e., using operators) and, sometimes, searches on LinkedIn or other sites that allow a logical combination of terms.
The word “Boolean” means the logic of AND, OR, and NOT. It was an essential part of Google back in 2008 when the term “Boolean Strings” came into use. But as you will observe:
On Google, using ORs is no longer advised Google does not strictly follow formal Boolean logic any longer.