The term 'rfac' in Fortran appears to be a user-defined function or variable, as there is no standard function by that name. Users suggest performing a text search across the entire codebase to locate its definition and instances of use, which can provide clarity on its purpose. A common method for this is using the 'grep' command in Linux to identify all occurrences of 'rfac'. This approach can help in understanding how 'rfac' interacts with other parts of the code. Overall, the discussion emphasizes the importance of examining the code context to unravel the mystery of 'rfac'.