Reversi terminology

Reversi Glossary

What makes an X-square risky? Why does a quiet move beat a big flip? Find the terms used in the rules, strategy and history of Reversi, grouped by when you’ll encounter them.

The board and discs

Disc: A playing piece that is black on one side and white on the other. A disc never leaves its square once placed, but it can change color many times.
Starting position: The four discs in the center squares at the start of every game, two of each color, with each color on a diagonal. Black moves first.
Square names: The way this guide labels squares. Columns run a to h from left to right and rows run 1 to 8 from the top, so a1 is the top-left corner and h8 is the bottom-right.
Disc count: The number of discs showing each color. It decides the game at the end and means little before then, because discs keep changing sides.
Othello: The trademarked name under which the modern rules were published in Japan in 1973. LarkSpark plays by those rules and uses the older name, Reversi.

Moves and flips

Trap: Enclosing a line of opposing discs between two of your own, with no gaps. The line can run across, up and down, or along a diagonal.
Bracket (outflank): Other names for a trap. Rulebooks often say that the disc you place and the one at the far end bracket, or outflank, the discs between them.
Flip: Turning a trapped disc over to the other color. Every disc you trap flips, in every direction at once, and you don’t get to choose.
Legal move: Placing a disc on an empty square where it traps at least one opposing disc. LarkSpark marks your legal squares on the board.
Pass: A skipped turn when a player has no legal move. You can’t choose to pass, and LarkSpark skips the turn for you.
Wipeout: A game that ends with every disc on the board showing one color. It can happen long before the board is full, because once one color is gone neither player can trap anything.

Squares and regions

Corner: One of the four squares a1, h1, a8 and h8. A disc there can never be flipped, which makes corners the most valuable squares on the board.
X-square: A square diagonally next to a corner: b2, g2, b7 or g7. Playing there while the corner is empty often gives your opponent the way in.
C-square: An edge square right beside a corner, such as b1 or a2. It is a smaller risk than an x-square, because it can only be attacked along that edge.
A-square: An edge square two steps from a corner, such as c1 or a3. It sits between a c-square and a b-square.
B-square: One of the two middle squares of an edge, such as d1 or e1. Read along any edge, the squares run corner, C, A, B, B, A, C, corner.
Edge: The outside rows and columns of the board. An edge disc can only be trapped along the edge, so it is harder to flip than a disc in the middle.
Sweet sixteen: The middle sixteen squares, from c3 to f6. Staying inside them in the opening keeps you away from the edges and the squares near the corners.
Region: A group of empty squares cut off from the other empty squares late in the game. Each region is its own small fight over who moves last.
Odd and even regions: A region with an odd or an even number of empty squares. The player who moves first in an odd region also moves last in it, so you play into odd regions and leave even ones alone.

Strategy

Opening: The first dozen or so moves, played mostly inside the sweet sixteen. The word can also mean a named sequence of starting moves, such as Tiger or Rose.
Parallel opening: One of White’s three replies to Black’s first move. After Black plays f5, it is f4. It is generally thought to be the weakest of the three.
Perpendicular opening: One of White’s three replies to Black’s first move. After Black plays f5, it is d6. It is a sound choice.
Diagonal opening: One of White’s three replies to Black’s first move. After Black plays f5, it is f6. It is a sound choice.
Mobility: The number of legal moves you have. A player with many moves can wait, and a player with few is eventually forced onto a bad square.
Frontier disc: A disc that touches an empty square. Your frontier discs are what your opponent plays against, so fewer of them means fewer moves for the other side.
Quiet move: A move that adds little or nothing to your frontier. The best ones flip a single disc that is already surrounded.
Loud move: A move that flips many discs facing empty squares. It gains discs for the moment and hands your opponent new places to play.
Wall: A long line of your discs facing empty squares. Every disc in it is a frontier-disc, so a wall gives your opponent mobility.
Wedge: A disc played into a gap between two groups of your opponent’s edge discs. It can’t be trapped by the discs beside it, and it attacks both ways along the edge.
Stable disc: A disc that can never be flipped again, such as one in a corner. Stability spreads outward from corners along the edges.
Tempo: A spare move you can make without hurting your position. It hands the turn back and makes your opponent use up one of their safe moves.

The endgame

Endgame: The last phase of play, from about a dozen empty squares to the final move. This is when the disc-count starts to matter.
Parity: Arranging to make the last move in each region. The last move there can’t be answered, so the discs it flips tend to stay flipped.
Endgame counting: Working out the final score of a line of play instead of judging it by feel. A move that flips five discs is a swing of eleven, and a pass means one player moves twice.
Draw: A game that ends with both players showing the same number of discs. The ending rules explain how LarkSpark scores a finished game.