In an elementary cellular automaton, each cell can appear in one of two possible states (depicted here as light and dark), with a rule determining the state of each cell based on its three northern neighbors. Each of the three neighbors can form one of eight possible sequences, ordered here according to the Wolfram Code:
as described by Stephen Wolfram in 1983. Each of these eight sequences can be set to result in one of two possible states; hence, there are a total of \(2^8 = 256\) possible rules. Each rule can be represented as a 8 digit binary string. The name of each rule is decided by the base 10 equivalent of this bit string.
Some rules are particularly interesting, including
Rule 30 which is chaotic,
Rule 54 which is believed to be universal, and
Rule 90 which generates the Sierpiński triangle from a single starting cell.