Traditionally, outside of Perl,

• Functions:

  returned values that were used as a part of the calling expression.

  Preferably they do not have side-effects.

• procedures:

  Returned only status. True/false, an error code or an exception.

  Usually side-effectful.

• subroutine:

  A generic term covering both and more.

I'm not sure if there is any language that actually enforced these rules. Didn't Pascal complain if you tried to return a value from a procedure?