The travel version of the game Mastermind.
It is the same game as Mastermind, but since it is smaller, the code-breaker only has 6 rows in which to guess the solution, instead of the usual 10 in the original version.
In Mini Mastermind, one player is the code-maker, and the other player is the code-breaker. The code-maker makes a code out of any combination of 4 colors (out of 6 possible colors). The code-breaker has 6 guesses to figure out the code.
After each code guess, the code-maker gives a clue, by placing a black peg for every correct color in the correct position, and placing a white peg for every correct color, in the wrong position.
Players generally switch roles after the code is broken or the code-breaker failed to solve the solution. Generally after the second play after roles were switched, the winner is the one who solved the code in the fewest amount of guesses.
A common version came in a small 2" X 5" plastic box with a playing board cover is encased in a slipsleeve. All of the components are kept neatly inside the box.