The DICT Development Group

  UTSL
   //, n.
  
      [Unix] On-line acronym for ?Use the Source, Luke? (a pun on Obi-Wan
      Kenobi's ?Use the Force, Luke!? in Star Wars) ? analogous to RTFS (sense
      1), but more polite. This is a common way of suggesting that someone would
      be better off reading the source code that supports whatever feature is
      causing confusion, rather than making yet another futile pass through the
      manuals, or broadcasting questions on Usenet that haven't attracted
      wizards to answer them.
  
      Once upon a time in elder days, everyone running Unix had source. After
      1978, AT&T's policy tightened up, so this objurgation was in theory
      appropriately directed only at associates of some outfit with a Unix source
      license. In practice, bootlegs of Unix source code (made precisely for
      reference purposes) were so ubiquitous that one could utter it at almost
      anyone on the network without concern.
  
      Nowadays, free Unix clones have become widely enough distributed that
      anyone can read source legally. The most widely distributed is certainly
      Linux, with variants of the NET/2 and 4.4BSD distributions running second.
      Cheap commercial Unixes with source such as BSD/OS are accelerating this
      trend.