One spade

As an opening

• An opening of 1♠ promises 4 or 5 ♠s, depending whether a 4 or 5-card major is being used. However, even in a 4-card major system, a 1♠ opening normally shows 5 ♠s since lower openings are preferred with 4-card suits.

As a response

• A 1♠ response to a natural opening shows 4 ♠s and 6+ HCPs. It is forcing for one round.

As an overcall

• A 1♠ overcall normally specifies 5 good ♠s (occasionally 4 very good ♠s) and 8-16 HCPs.

Bids
1♣-1♦-1♥-1♠-1NT 2♣-2♦-2♥-2♠-2NT 3♣-3♦-3♥-3♠-3NT 4♣-4♦-4♥-4♠-4NT 5♣-5♦-5♥-5♠-5NT 6♣-6♦-6♥-6♠-6NT 7♣-7♦-7♥-7♠-7NT