An integer variable containing an address in memory, ie "pointing" to it. Some ProgrammingLanguages even permit you to do Pointer arithmetics. However, that is a very error prone task (in fact, bug source #1). Therefor, Pointer arithmetic is nowadays frowned upon unless you are doing low level systems programming.
Nowadays, if you aren't writing a kernel or hardware driver, you should be using a ProgrammingLanguage that has GarbageCollection and frees you from the arduous task of keeping track of your memory. A common requirement of such languages is that programs don't perform arbitary bitswise opertaions on pointers, so that the garbage collector can find and follow pointers. This requirement is common implemented via the type system.
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