The bid shows support in the major opening. The strength is up to the partnership. In the past this bid showed 16Hcp+, but in the last years the strength has been as low as limit. The version presented here is GameForcing. Further bids are as follows:
1H-2NT
3C : Side suit & extra strength (May be a 3 card suit)
3D : Side suit & extra strength (May be a 3 card suit)
3H : Extra length & extra strength.
3S : Side suit & extra strength.
3nt : 18-19NT / Could be agreed as void in spade?
4C : Void in club.
4D : Void in diamond.
4Hj : Minimum.
4S : Void in spade (Not a good bid if you ask me)
1S-2NT
3C : Side suit & extra strength (May be a 3 card suit)
3D : Side suit & extra strength (May be a 3 card suit)
3H : Extra length & extra strength.
3S : Extra length & extra strength.
3nt : 18-19NT
4C : Void in club.
4D : Void in diamond.
4H : Void in heart.
4S : Minimum.
*When your partner bids a sidesuit I bid 3 in the opening
suit to ask for a singleton. The opener bid the suit he has
a singleton in.
*3NT is a "resting" bid. You demand a cuebid from your
partner. You could have a hand where you want to hear if
your partner denies a club cuebid.