The Jargon File (version 4.4.7, 29 Dec 2003):

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.


The Free On-line Dictionary of Computing (30 December 2018):

memory leak
core leak
leaky heap

    A leak in a program's dynamic store
   allocation logic that causes it to fail to reclaim memory in
   the heap after it has finished using it, eventually causing
   the program to fail due to lack of memory.

   These problems were severe on older machines with small,
   fixed-size address spaces, and special "leak detection" tools
   were written to diagnose them.

   The introduction of virtual memory made memory leaks a less
   serious problem, although if you run out of virtual
   memory, it means you've got a *real* leak!

   See aliasing bug.

   [Jargon File]

   (2003-10-07)