- the edge or boundary of the playing field, and
- a manner of scoring runs.
Edge of the field 
The boundary is the edge of the playing field, or the physical object marking the edge of the field, such as a rope or fence. In low-level matches, a series of plastic cones are often used. Since the early 2000s the boundaries at professional matches are often a series of padded cushions carrying sponsors' logos strung along a rope. If it is moved during play (such as by a fielder sliding into the rope) the boundary is considered to remain at the point where that object first stood.
When the cricket ball is inside the boundary, it is in play. When the ball is touching the boundary, grounded beyond the boundary, or being touched by a fielder who is himself either touching the boundary or grounded beyond it, it is out of play and the batting side usually scores 4 or 6 runs for hitting the ball out of play. Because of this rule, fielders near the boundary attempting to intercept the ball while running or diving, often flick the ball back in to the field of play rather than pick it up directly, because their momentum could carry them beyond the rope while holding the ball. They then return to the field to pick the ball up and throw it back to the bowler.
Scoring runs 
A boundary is the scoring of four or six runs from a single delivery with the ball reaching the boundary of the field. Occasionally there is an erroneous use of the term boundary as a synonym for a "four". For example sometimes commentators say such as "There were seven boundaries and three sixes in the innings." The correct terminology would be "There were ten boundaries in the innings of which seven were fours and three were sixes".
Four runs are scored if the ball bounces before touching or going over the edge of the field and six runs if it does not bounce before passing over the boundary in the air. These events are known as a four or a six respectively. When this happens the runs are automatically added to the batsman's and his team's score and the ball becomes dead. If the ball did not touch the bat or a hand holding the bat, four runs are scored as the relevant type of extra instead; six runs cannot be scored as extras, even if the ball clears the boundary, which is in any case extremely unlikely. Prior to 1910, six runs were only awarded for hits out of the ground.
Four runs (or more) can also be scored by hitting the ball into the outfield and running between the wickets. Four runs scored in this way is referred to as an 'all run four' and is not counted as a boundary.
Four runs are scored as overthrows if a fielder gathers the ball and then throws it so that no other fielder can gather it before it reaches the boundary. In this case, the batsman who hit the ball scores however many runs the batsmen had run up to that time, plus four additional runs, and it is counted as a boundary. If the ball has not come off the bat or hand holding the bat, then the runs are classified as 'extras' and are added to the team's score but not to the score of any individual batsman.
The scoring of a four or six by a good aggressive shot displays a certain amount of mastery by the batsman over the bowler, and is usually greeted by applause from the spectators. Fours resulting from an edged stroke, or from a shot that did not come off as the batsman intended, are considered bad luck to the bowler. As a batsman plays himself in and becomes more confident as his innings progresses, the proportion of his runs scored in boundaries often rises.
An average first-class match usually sees between 50 and 150 boundary fours. Sixes are less common, and usually fewer than 10 (and sometimes none) will be scored in the course of a match (especially a Test match).
The record for most sixes in a Test match innings is 12, which was achieved by Pakistani all-rounder Wasim Akram during an innings of 257 not out against Zimbabwe in October 1996 at Sheikhupura. The One Day International record for most sixes hit in an innings is held by Shane Watson who hit 15 sixes against Bangladesh in Dhaka in April 2011.
Adam Gilchrist currently holds the record for most sixes in a Test career (100 as of March 2009). Shahid Afridi holds the record for most sixes in an ODI career (293 of 296 matches as of 329 Matches Till November 2011).
The record for the most sixes in a Test match is 27, which occurred during a 2006 Test match between Pakistan and India at the Iqbal Stadium in Faisalabad. In their first innings, Pakistan hit eleven sixes. India hit nine in their first innings. Pakistan hit seven more sixes in their second innings.
The record for the most sixes in a One Day International is 31, which was achieved in a match between India and New Zealand at AMI Stadium in March 2009. India hit 18 sixes in their innings and New Zealand hit 13. The equivalent record in Twenty20 Internationals was set on the same ground and on the same tour, 24 sixes were hit during the Twenty20 International match between India and New Zealand on 25 February 2009.
6 Sixes in an over 
On 31 August 1968, Garfield Sobers became the first man to hit six sixes off a single six-ball over in first-class cricket. The over was bowled by Malcolm Nash in Nottinghamshire's first innings against Glamorgan at St Helen's in Swansea. Nash was a seam bowler but—somewhat rashly, as it turned out—decided to try his arm at spin bowling. This achievement was caught on film.
On 16 March 2007, in a match between South Africa and the Netherlands at the 2007 Cricket World Cup, Herschelle Gibbs became the first person to hit six sixes off an over in a One Day International match. The over was bowled by Dutch leg-spinner Daan van Bunge.
On 19 September 2007, in a match between England and India, Indian cricketer Yuvraj Singh hit six sixes off a single six-ball over in a Twenty20 international cricket match during the inaugural ICC Twenty20 World Cup in Durban, South Africa. The bowler was Stuart Broad of England.
- "Ask Steven", 23 January 2006 Retrieved 7 July, 2011
- Most sixes in career (Tests)
- Most sixes in career (ODIs)
- "West Indies' Chris Gayle creates Test history with opening six". BBC Sport. Retrieved 2012-11-14.
- Wisden 1969
- Sir Garfield Sobers 6 sixes in a row - BBC Wales video (streamed)
- "Gibbs matches Sobers in easy win". BBC Sport. 2007-03-16.
- BBC, accessed 24 April 2013