After 2 years, I'm finally going to take a stab at explaining cricket, using an analogy to an American game which has absolutely no similarities.
Imagine playing baseball, except the bat is flat on one side, the ball is smaller, the pitcher runs up and throws overhand, and the ball bounces before it reaches the batter. Sound like a girls' game? Consider that the ball is much denser, is often thrown in excess of 90mph, and can bounce in just about any direction. The batter--sorry, batsman--looks like a cross between Hannibal Lecter and an ice hockey goalie, in a full face mask, thick gloves, and full body armor. If the ball hits the batsman, the umpire may give the batsman a run, but more often will call him out for "leg before wicket."
The wicket is a set of three wooden stakes between the batter and the catcher -- or wicket-keeper -- with two "balls" (that aren't balls at all) resting on top. The pitcher -- bowler -- tries to knock one of the balls off the wicket, which is equivalent to a "strike out." The batsman, then, must "protect the wicket" but has to do so with the bat -- if he uses his body, and the ball would have hit the wicket, then he is out.
There are also two bowlers who switch every six balls. (This is called an "over" because the umpire calls "over!") When this happens, everything switches sides, so the other batsman now becomes the striker.
If a fielder tags the wicket while the runner is off base, he has been "run out" -- although in cricket the "base" is really just a chalk line (and is referred to as a "popping crease" for reasons not worth going into. I should also mention that every ball is in play, so even if the ball is wide, or the batsman doesn't hit it, or even if it is called "no ball" (eg if it bounces twice), the batsman can still run to the other base. However, that usually only happens if the wicketkeeper misses the ball--otherwise he just gets run out. The umpire can also award runs for wide balls or no balls ("byes"). If the ball leaves the the oval field, the batsman automatically gets 4 or 6 runs, depending on if the ball bounced first or not.
Each side has 11 men, and each man gets a turn at bat, so the inning is over when 10 men are out. (You can't leave a single runner.) This can take days--literally--and there are two innings per game. Scores are in the hundreds, with individual players often scoring a "century" (100 runs or more). If both teams have completed both innings, then the team with the most runs wins. (If the second team has more runs in the second inning, they don't need to finish the inning.) However, if the game goes on for more than five days, the game is a "draw" no matter how many runs were scored! For that reason, if a team is ahead it may ends its innings in order to give the other team time to finish. (Similarly, if the first team is more than 200 runs ahead at the end of the first inning, they can order the second team to go first in the second inning.)
Unfortunately, the pressures of modern life often mean a 5-day match is not possible, and so there are shorter variations which usually involved "limited overs." For example, in Twenty20, only 20 overs per inning are allowed. (The other "20" referrs to the number of countries involved.) Cricket started in the 16th century, and was England's national sport by the 18th century. In the 19th century, they exported cricket to the rest of the empire, and now England is regularly beaten in international matches. One of the most famous matches is "The Ashes," which date back to 1882 when a a British newspaper published an obituary after Australia beat England on English soil, stating that "English cricket had died, and the body will be cremated and the ashes taken to Australia." The next year, England went to Australia to "regain the Ashes" and the name stuck. England was even presented with an urn, which is on display at Lord's cricket ground, one of the most famous pitches in the world.