It depends on the context. Binary is a base 2 numbering system, where all numbers are represented by combinations of only 2 digits 0 & 1, instead of the normal 10 digits (0-9.) Digital often means electronic as opposed to some other medium. A digital newspaper vs. a print newspaper. A digital signal is different from an analog signal in that it is binary in nature, either off or on (0 or 1). It would have a squarish wave form. When it's on it would have a consistent amplitude. An analog signal is different because it is would have a curved wave form. They both can transmit information it's a matter of interpreting it on the receiving end.
So, in a way, they can sorta be used interchangeably, but your question is like asking what is the difference between a hippo and a dna strand.