When we say a program leaks memory, say a new without a delete in c++, does it really leak? I mean, when the program ends, is that memory still allocated to some non-running program and can't be used, or does the OS know what memory was requested by each program, and release it when the program ends? If I run that program a lot of times, will I run out of memory?
As far as I know, on most OS when a program is started it receives a defined segment of memory which will be completely liberated once the program is ended.
Memory leaks are one of the main reason why garbage collector algorithms were invented since, once plugged into the runtime, they become responsible in reclaiming the memory that is no longer accessible by a program.
Memory leaks don't persist past end of execution so a "solution" to any memory leak is to simply end program execution. Obviously this is more of an issue on certain types of software. Having a database server which needs to go offline every 8 hours due to memory leaks is more of an issue than a video game which needs to be restarted after 8 hours of continual play.
The term "leak" refers to the fact that over time memory consumption will grow without any increased benefit. The "leaked" memory is memory neither used by the program nor usable by the OS (and other programs).
Sadly memory leaks are very common in unmanaged code. I have had firefox running for a couple days now and memory usage is 424MB despite only having 4 tabs open. If I closed firefox and re-opened the same tabs memory usage would likely be <100MB. Thus 300+ MB has "leaked".