One of 0/0, 0*infinity, infinity - infinity, 0^infinity, 1^infinity, infinity^0, or 0^0. The actual numerical values of these are not well defined; they depend on where the 0's and infinities came from.

Note: ariels is correct that this is not precisely accurate; it would be more accurate to say that the _limits_ of these quantities are indeterminate forms, not the quantities themselves. These quantities are always undefined; their limits, however, can have values. (Please see 0/0 for a more detailed explanation.)