If you have
function y = YourFunction(x)
then y is the "formal output argument" -- the name of the output argument as it is called inside the function. Likewise, x is the "formal input argument" -- the name of the input argument as it is called inside the function.
This contrasts with the use of this routine, which might look like
velocity = YourFunction(0:.01:15)
in which the 0:.01:15 would be the actual input argument, and "velocity" would be the actual output argument.
