An interpreter, in the computational/mechanical sense, is a device that operates over a set of instructions and performs some action.
A computer is an interpreter; so is a ribosome.
The philosophically interesting thing about these mechanisms is that they illustrate ways in which physical systems can implement semantics. A triplet of DNA codons means a particular amino acid, but only by virtue of the structure of its interpreter (the ribosome) [cite Hofstadter piece]. "ADD A to B" means a particular process of electrical activity as well as its result.
Humans of course are vastly more complicated but they share this quality of being both physical/mechanical devices and interpreters of meaning.