Splinter bids are an important part of any bidding system. They show 4 card support for partner’s suit and a singleton or void in the splinter suit. So which bids are splinter bids? When the opponents are silent, new suits at the minimum level are one round forces and jumps in a new suit show a strong 6+ card suit, are forcing to game and show slam interest. The next level bids are the double jumps like 3S, 4C and 4D over 1H. These are the splinter bids and they show 11+ hcp and the shortage. Do not count shape points because the shortage is explicitly shown.
In the hand shown in the next column, EW were not playing splinter bids and failed to solve the bidding problem. East made cue raise and West signed off in 4H showing a minimum. West should have cue bid 4C to suggest more than minimum since they have 12hcp + 3 shape points
East tried RKC but couldn’t find an excuse to bid the slam since there appeared to be spade losers and an empty diamond suit.
Look how a splinter bid would solve the bidding problem. Over 2S, East could bid 3C to show a club suit and force to game. Thus, 4C is not needed as a stronger bid and is treated as a splinter bid. Over 4C, West now counts two less club losers ( i. e. four losers rather than the initial six losers) and so cue bids 4D to show interest in slam. East has 14 hcp and has only shown 11+ hcp so they have a king in extra values which they have not yet shown and should cooperate in bidding a slam by either cue bidding 4S or bidding RKC. The key insight is that with a king, or more, better than the minimum that you have shown so far, you must try to avoid making a minimum bid. Experts want to have this kind of cuebid conversation about slam suitability and that is why they don’t play Gerber.