The value of *load-pathname* must always be a pathname or nil. The value of *load-truename* must always be a physical pathname or nil.
During a call to load, *load-pathname* is bound to the pathname denoted by the the first argument to load, merged against the defaults; that is, it is bound to (pathname (merge-pathnames filespec)). During the same time interval, *load-truename* is bound to the truename of the file being loaded.
At other times, the value of these variables is nil.
If a break loop is entered while load is ongoing, it is implementation-dependent whether these variables retain the values they had just prior to entering the break loop or whether they are bound to nil.
The consequences are unspecified if an attempt is made to assign or bind either of these variables.
The file system.