-in-a-row is a generalization of tic-tac-toe
in which players alternate placing pieces (typically Xs for the first player and
Os for the second) on an 
board. The first player to get 
pieces in a row (vertically, horizontally, or diagonally)
is the winner.
n-in-a-Row
See also
Connect-Four, Gomoku, Qubic, Tic-Tac-ToeExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "n-in-a-Row." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/n-in-a-Row.html