While studying about TCP i notice that is very similar to Go-Back-N, but ,i think i'm missing something very important:

In http://www.ccs-labs.org/teaching/rn/animations/gbn_sr/ we can see that in GBN , the server gives ack to every packet that coming.

In https://www.scribd.com/doc/2631780/56/Is-TCP-Go-Back-N-or-Selective-Repeat p.65, it says:

Is TCP Go-Back-N or Selective Repeat?

 similarity of TCP with Go-Back-N

1.TCP :cumulative ack for the last correctively received, in-order seg
2.cumulative and correctly received but out-of-order segs are not individually acked ⇒ TCP sender need only maintain SendBase and NextSeqNum

What is the meaning of cumulative ACK? and what is the difference between selective ACK? and why TCP uses the first one?