Principal variation
The principal variation is the line of best play for both sides that an engine has found, shown as a sequence of moves and tied to the evaluation it reports.
Also called: PV
When an engine analyzes a position, it does not only give one move. It shows the principal variation, often shortened to PV, which is the sequence of moves it expects if both sides play the best they can find. The first move of the line is the engine’s recommendation, and the later moves explain the idea behind it by showing how the opponent should respond and what follows.
Reading the PV is one of the most useful ways to learn from an engine. If you do not understand why a move is best, play through the line on your board and watch what it achieves, such as winning material, forcing a trade into a won endgame or creating a threat that cannot be parried. Many engines let you display several lines at once, which is helpful when two moves seem close.
Remember that a PV is only as reliable as the depth the engine reached. At a low depth the later moves may change, and in complicated positions the line is not guaranteed to be what a human opponent will choose. Treat it as a strong suggestion that deserves your attention.
A neighboring idea is Engine analysis. Engine analysis is the use of a chess program to search a position and report which moves are strongest, along with a numeric evaluation and the lines it expects both sides to follow.
A neighboring idea is Minimax. Minimax is a decision method in which one side tries to maximize the evaluation while the opponent tries to minimize it, forming the basis of how traditional chess engines choose moves.
Compare it with Alpha-beta pruning. Alpha-beta pruning is a search technique that skips branches of the move tree that cannot change the minimax result, letting engines look much deeper using the same amount of computing time.
Computer terms such as "Principal variation" are most useful next to a coach who reads your games with you, which is how a first lesson with George Li works.
Related terms
Search depth is how many moves ahead an engine has looked in a position, counted in half-moves called plies, and deeper searches generally give more reliable evaluations and moves.
An evaluation is a numerical judgment of who stands better in a position, usually given in pawns from White’s point of view, where positive favors White and negative favors Black.
A chess engine is a computer program that searches positions and evaluates moves, usually playing and analyzing far stronger than any human, and it is used for analysis, preparation and play against a machine.
Engine analysis is the use of a chess program to search a position and report which moves are strongest, along with a numeric evaluation and the lines it expects both sides to follow.
Minimax is a decision method in which one side tries to maximize the evaluation while the opponent tries to minimize it, forming the basis of how traditional chess engines choose moves.
Post-game analysis is the discussion or private review held right after a game, in which both players or one player alone retrace the moves and identify the turning points, missed ideas and lessons.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
How much does chess coaching cost?
Published rates for private, group and subscription chess coaching, with the source and the date of each.
A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.