In computing the term core is most frequently found in the phrase core dump , which derives from magnetic core memory . Around here, core usually means The Tcl Core -- the C implementation of Tcl managed by the Tcl Core Team. Accordingly, the term "core command" refers to a built-in Tcl command.
The use of the term "core" carries over to other programs. A core command of incr tcl would be one of the commands from the source distribution variations of that software as maintained by its project maintainers.
A core dump is the memory image that is produced if a program crashes and dumps core. A core dump can be a valuable help for debugging the crash, if you are an expert in understanding C stack traces and particularly if you configured Tcl and the extensions with -enable-symbols.
DKF: A core dump is like the corpse of a process on Unix. Sometimes, you just have to carry out an autopsy to satisfy the coroner...