memory leak n. An error in a program's dynamic-store allocation logic
   that causes it to fail to reclaim discarded memory, leading to eventual
   collapse due to memory exhaustion. Also (esp. at CMU) called {core
   leak}. These problems were severe on older machines with small,
   fixed-size address spaces, and special "leak detection" tools were
   commonly written to root them out. With the advent of virtual memory, it
   is unfortunately easier to be sloppy about wasting a bit of memory
   (although when you run out of memory on a VM machine, it means you've
   got a _real_ leak!). See {aliasing bug}, {fandango on core}, {smash the
   stack}, {precedence lossage}, {overrun screw}, {leaky heap}, {leak}.


Source: The Jargon File