The base pointer on the x86 architecture serves two purposes:

1) The address of the base pointer (stored in EBP) is a reference to the base of the current stack frame, enabling you to access function arguments and local variables as an offset from the address in EBP.

2) The value stored at the address EBP contains is the stack address of the previous stack frame’s base address. This is setup in the stack prologue when you:

; Snippet of the stack prologue - Intel Syntax 

push ebp        ; Store the calling functions base pointer on the stack, often
                ; referred to as the 'Saved Frame Pointer (SFP)'

mov ebp, esp    ; Set the base pointer for the function that was just entered
                ; by setting it equal to the top of the stack. 

If you look at the EBP register in GDB you will see that it looks like a list of stack addresses. The base address for the current stack frame, holds the base address of the previous stack frame which holds the base address of the stack frame before that and so on. At the point in time when we pop ebp in the epilogue, the top of the stack will point to the base of the current stack frame (thanks to the instruction just prior to this one), i.e. ESP and EBP will point to the same address, when we pop ebp we take the value of the address that ESP is pointing to i.e. The value at the address address of the base pointer (the previous stack frame’s base address) and we place it inside EBP thus restoring EBP for the previous stack frame ready for us to return to the calling function.