Code golf is a type of recreational computer programming competition in which participants strive to achieve the shortest possible code that solves a certain problem.
Source: Wikipedia
I've recently found some very interesting code golf examples on codegolf.stackexchange.com:
Snake
Task: Recreate the classic snake Game.
The shortest answer is written in Ruby in 316 characters, the longest is written in Java in 2239 characters.
Here is a Python answer with 818 characters:
import pygame as p
from random import randint as r
p.init();l=20
c=p.time.Clock()
dp=p.display;w=p.display.set_mode((500,500))
C=p.Color;b=C(0,0,0);g=C(0,255,0)
D=(0,1);U=(0,-1);L=(-1,0);R=(1,0)
S=[R];d=R;n=[]
O=lambda t:{U:D,R:L,D:U,L:R}[t]
def Q(e):print "Score: %i"%(len(S)-1);p.quit()
def K(e):global d;_={276:L,273:U,274:D,275:R}.get(e.key,(0,0));d=not _==O(d) and _ or d
def N(S):[p.draw.rect(w,g,[x[0]*l,x[1]*l,l,l]) for x in S+n]
def M():n=(r(0,24),r(0,24));return n not in S and n or M()
A=lambda s,o:tuple(x+y for x,y in zip(s,o))
n=[M()]
while True:
w.fill(b);[{12:Q,2:K}.get(e.type,lambda e:e)(e) for e in p.event.get()]
if not (0<=S[-1][0]<25 and 0<=S[-1][1]<25) or A(S[-1],d) in S: Q(e)
if A(S[-1],d) in n: S.append(A(S[-1],d));n=[M()]
else: S.append(A(S[-1],d));S.pop(0)
N(S);dp.update();c.tick(6)
Matrix determinant
Task: Calculate the determinant of a \(n \times n\) matrix.
Solution in J (61 characters):
-/>([:+/#(([{.<:@[}.])[:*//._2,\2#])])&.>(|.;])".];._2[1!:1[3
Solution in Python (198 characters):
t=input()
e=enumerate
p=lambda t:t and((b+[a],j+i)for i,a in e(t)for b,j in p(t[:i]+t[i+1:]))or[([],0)]
print sum(reduce(lambda t,(i,r):t*r[i],e(p),1-i%2*2)for p,i in p([t]+[input()for x in t[1:]]))
Factorial
Task: Find the factorial of a number.
J (12 characters):
f=:*/@:>:@i.
Python (27 characters):
f=lambda x:0**x or x*f(x-1)
By the way, the shortest Java solution is 85 characters long^^.