Jaffa (also corker) 
an exceptionally well bowled, practically unplayable delivery, usually but not always from a fast bowler. Jayadevans system
an unsuccessful proposal for a rain rule, as an alternative to the Duckworth-Lewis system. Has never been used in professional cricket. Jockstrap (also jock strap)
underwear for male cricketers, designed to securely hold a cricket box in place when batting or wicket keeping. Just not cricket
see its (just) not cricket

K
Keeper
see wicket-keeper

Keep wicket
1. For a wicketkeeper to field. 2. "Keep wickets in hand", which is when a batting team tries to have relatively few of its batters get out. Usually done so that more run-scoring risks can be taken near the end of their innings in a limited-overs match, since they will have many batters left and only a few balls left. King pair
see Golden pair. Knock
a batsmans innings. A batsman who makes a high score in an innings can be said to have had a "good knock". Knuckle ball
A type of delivery where the fast bowler holds the ball on the knuckles of their index and middle finger. A type of slower ball. Kolpak
an overseas player who plays in English domestic cricket under the Kolpak ruling. Kwik cricket
(or quick cricket) An informal version of cricket with sped-up rules, specifically designed to introduce children to the sport. L
Lappa
The Indian version of the hoik. Comes from the English lap, an old term for a stroke somewhere between a pull and a sweep.
Wisden excludes records set in contrived circumstances from its official lists. Cordon
(or slips cordon)Collective term for multiple fielders in the slips. Sometimes also includes gully. Corridor of uncertainty
a good line. The corridor of uncertainty is a notional narrow area on and just outside a batsmans off stump. If a delivery is in the corridor, it is difficult for a batsman to decide whether to leave the ball, or play at it defensively, or play an attacking shot. The term was popularised by former England batsman and latterly commentator, Geoffrey Boycott. County cricket
the highest level of domestic cricket in England and Wales. Cover
(or the covers)
1. A fielding position on the off side, forward of point and squarer than mid-off. A cover fielder situated closer to point than usual is known as cover point, whilst one which is closer to mid-off is known as extra cover. The plural term the covers refers to all these variants collectively. 2. A waterproof assembly or tarpaulin used by the ground staff to protect parts of the field from rain (usually the pitch, square and run ups). Cow corner
the area of the field (roughly) between deep mid-wicket and wide long-on. So called because few legitimate shots are deliberately aimed to this part of the field, so fielders are rarely placed there – leading to the concept that cows could happily graze undisturbed in that area.