For all practical purposes

For all practical purposes is a slogan used in physics to express a pragmatic attitude. A physical theory might be ambiguous in some ways — for example, being founded on untested assumptions or making unclear predictions about what might happen in certain situations — and yet still be successful in practice. Such a theory is said to be successful FAPP.
FAPP is also emerging as a valuable concept and approach in mathematics with a major title by the name "For All Practical Purposes: Mathematical Literacy in Today's World".
There is also a profound joke about FAPP: