Connect 4 Glossary

The board and discs

Board

The upright grid, seven columns wide and six rows tall, with 42 spaces. It is also called the grid.

Column

One of the seven vertical stacks of spaces. On your turn you choose a column, and your disc takes its lowest empty space.

Row

One of the six horizontal levels of the board. Rows are counted from the bottom, so the first discs played land on row one.

Disc

A playing piece. One player has red discs and the other yellow. Hasbro’s instructions call them checkers.

Drop

To make a move by placing one disc in a column. The disc falls to the playable-space and stays there for the rest of the game.

Playable space

The lowest empty space in a column, the only one a disc can reach right now. A board has at most seven of them at a time.

Full column

A column holding six discs. Nobody can play there again.

Center column

The fourth of the seven columns. Its spaces belong to more possible lines of four than those of any other column, which is why strong players take it early.

First player

The player who makes the opening move. On LarkSpark that is always Red, and Yellow is the second player.

Lines and winning

Line of four

Four discs of one color in an unbroken line across, up and down, or on a diagonal. The first player to make one wins, and a longer line counts too.

Diagonal

A slanting line of spaces that climbs one row for each column it crosses, to the right or to the left. Diagonal lines are the ones new players miss most often.

Threat

A line of three with a fourth space that could still be filled. The word is also used for that empty space itself.

Block

Dropping a disc into the space your opponent needs to complete a line-of-four.

Draw

A game with no winner. It happens when all 42 spaces are full and neither player has a line of four.

Threats and tactics

Double threat

Two winning spaces at once. Your opponent can block only one of them per turn, so a double threat usually wins. Also called a fork.

Fork

Another name for a double-threat, most often used when one disc creates both threats.

Open three

Three discs in a row with an empty space at each end. If both ends are playable, it is a double-threat.

Stacked threats

Two threats by the same player, one directly above the other in a column. When the column fills to the lower one, a block there opens the upper one.

Poisoned square

A playable-space you should leave alone because the space above it would win for your opponent. The rules chapter calls this watching the square above.

Forced move

A move you have to make, usually a block, because anything else loses at once.

Tempo

A turn, thought of as a unit of time. A move that makes your opponent answer with a forced-move gains a tempo, because you get to choose again.

Timing and the endgame

Endgame

The last phase of play, when most columns are full and each remaining move opens a space that matters.

Odd and even rows

Rows one, three and five are odd, and rows two, four and six are even, counting from the bottom. Late in the game the first player tends to get the odd spaces and the second player the even ones.

Odd threat

A threat whose empty space is on an odd row, in practice the third or fifth. Red, who moves first, usually wants these.

Even threat

A threat whose empty space is on an even row. Yellow, who moves second, usually wants these.

Zugzwang

Having to move when you would rather pass. With the safe spaces used up, the player to move must drop a disc under a poisoned-square and give the opponent the space above.

Follow-up

Answering a move by playing directly on top of it in the same column. The player who follows up collects every space on one set of rows.

Claimeven

Victor Allis’s name for the follow-up rule used by the second player, who waits for the opponent to take an odd space and then takes the even space above it.

Solving and variants

Perfect play

Choosing a best available move on every turn. It is a standard for proofs and computers, and no person manages it for a whole game.

Solved game

A game whose result under perfect-play is known. Connect 4 was solved in 1988: the first-player wins by starting in the center-column, as the history chapter explains.

Four in a row

A generic name for the game, used because Connect 4 is a Hasbro trademark. It also describes the winning line-of-four.

Pop Out

A Hasbro way to play in which a turn can pop a checker out of the grid instead of dropping one in. LarkSpark plays the original game, where discs never move once they land.