Brainfuck is an esoteric programming language created in 1993 by Urban Müller.
BrainFuck is executed on a memory array. By default, it's a 30k-cell-long array of 8-bit integers, but some other implementations are more flexible.
There are two registers : Instruction pointer and Memory Pointer.
Finally, there are 8 instructions:
">" : Move memory pointer to the right and go to next instruction
"<" : Move memory pointer to the left and go to next instruction
"+" : Increment memory cell and go to next instruction
"-" : Decrement memory cell and go to next instruction
"," : Read char from input and store in memory then go to next instruction
"." : Write memory value as ASCII char to output then go to next instruction
"[" : Go to next instruction if cell is not null, or to the matching closing "]" if null
"]" : Go back to the matching opening "[" if cell is not null, or go to next instruction if null
Go here to try the BF yourself: http://www.bf.doleczek.pl/