Terms you will meet in Four in a Row games and guides, explained briefly:
Four in a Row
The classic two-player connection game on a vertical 7x6 grid: drop discs, line up four in any direction to win. Known worldwide under many local and trademarked names.
Drop
A move: choosing a column so your disc falls to the lowest empty cell of that column. Each turn is exactly one drop.
Column
One of the 7 vertical tracks. A column accepts drops until it holds 6 discs; after that it is full and no longer a legal move.
Gravity
The rule that discs always sink to the bottom-most empty cell of their column and stack upward from there.
Four (winning line)
Four of your own discs in one straight line — horizontal, vertical or diagonal. Completing one wins the game immediately.
Line
Any of the 69 four-cell straight paths on the 7x6 grid: 24 horizontal, 21 vertical and 24 diagonal.
Open three
Three of your discs in a line where the fourth cell is empty and reachable on your next drop — an immediate threat your opponent must answer.
Open two
Two of your discs in a line with two empty cells — a developing threat that can grow into an open three.
Double threat
Two open threes at once. The opponent can block only one drop per turn, so a real double threat wins the game.
Center control
Playing the middle column early. The center cells belong to the most winning lines, and the solved winning openings all start there.
Board full
All 42 cells filled with no four-in-a-row on either side — the only drawing outcome in the game.
Solved game
A game whose perfect-play outcome is mathematically known. Four in a Row was solved in 1988: the first player wins, starting from the middle column.