Opener rebids his 6+ card suit:
South:
♠ A K 10 9 8 7 South North
♥ 8 5 1♠ 2♣
♦ A Q 7 2♠
♣ 5 2
South’s 2♠ bid after the 2/1 response shows a 6+ card suit.
However, if opener jumps in his original suit, it shows a solid 6+ card suit.
Opener rebids 2 NT:
This is not a "vague" bid. You must have the right stuff:
• No 6-card major; a balanced hand
• Points: 12-14 or 18-19 (with 15-17, open 1 NT)
West East
♠ K 8 7 ♠ A J 9
♥ A J 6 4 3 ♥ 8 5
♦ 6 4 ♦ K Q J 9 8
♣ K Q 9 ♣ A 7 6
West East
1♥ 2♦
2 NT 3 NT
If West had 18-19, then after East bid 3 NT, West would look for slam.
Note: Opener's second bid of 2 NT does not require stoppers in the unbid suits. This is controversial – some play opener's 2 NT rebid does require stoppers.