JE McGimpsey wrote...
Blank means blank, not containing a formula.
....

To be fair, this is one of Microsoft's more boneheaded mistakes.
ISBLANK likely got its name from the mnemonic returned by
CELL("Type",SomeRange), which returns "b" when the top-left cell in
SomeRange has nothing in it. Microsoft was able to figure out ISTEXT
rather than ISLABEL despite the fact that CELL("Type",...) returns
"l" (lower case L) when the top-left cell evaluates as a text string.
Further, most non-English variants of the ISBLANK function have names
that translate back into English as ISEMPTY. And, FWLIW, the
equivalent Lotus 123 function is named @ISEMPTY.