1NT  = Natural.

2♣  = 6+♦ weak or GF.

2♦   = 3 cards support. 9+ DH, no ambitions.

2♥   = 3 cards support. 5-8 DH.

2♠ =  6+♣ weak or 5+ ♣ GF.

2NT = 4+ cards support  or 3 cards support ambitions.

3m  = 6+ m. Limit.

3♠   = SPLINTER.

Purpose: to show  ♥ raise immediately. Play the minors from the right hand (the overcaller will be on lead).

All this, in the minds of developments after an overcall on 1 ♣ .