When playing the popular 2/1 GF system, the 1NT response needs to be addressed. In the old days, 1NT was 6-10. But, when a 2-level response shows about 13, the responder needs to cope with 11- and 12-point hands. Those are lumped into the 1NT response.
If partner opens 1
, and responder holds, say: 5
...
