Development
Development means bringing your pieces from their starting squares to active posts, usually by moving the knights and bishops out, castling and linking the rooks, so they can all contribute to the fight.
At the start of a game most of your army sits on the back rank, doing nothing. Development is the process of bringing it into play. Knights and bishops usually come out first, the king is tucked away by castling, and the rooks then find open or half-open lines. A well developed side can strike anywhere on the board, while an undeveloped piece is a spectator.
Simple habits help. Move each minor piece once, aim for squares where it influences the center, and avoid shuffling the same piece again and again. Do not bring the queen out early, because it becomes a target and the opponent develops with tempo against it. Only make a pawn move when it helps your pieces or fights for the center.
Development is also a measure. If you are further along than your opponent, you may be able to open the position and punish them. If you are behind, you should keep the position closed and finish catching up before anything opens.
The usual error is to stop thinking of development once the king is castled. Every piece, including the rook on the corner, should have a job before you start a plan elsewhere.
Also worth reading is Tempo. A tempo is a single move counted as a measure of time: gaining one means making a useful move that also forces the opponent to react, while losing one means spending a move that accomplishes nothing.
It sits close to Center control. Center control means influencing the central squares d4, d5, e4 and e5, with pawns, pieces or both, so that your forces move freely and the opponent has less room to operate.
Compare it with Opening principles. Opening principles are general guidelines for the first moves: control the center, develop knights and bishops quickly, castle early and avoid moving the same piece twice without reason.
Strategic ideas such as "Development" show up in your games as small decisions, move after move. A first lesson with George Li reviews those decisions and turns them into a study plan.
Related terms
A tempo is a single move counted as a measure of time: gaining one means making a useful move that also forces the opponent to react, while losing one means spending a move that accomplishes nothing.
A lead in development means having more of your pieces already active than your opponent has at the same moment, which usually gives a short window to open the position and attack before they catch up.
Piece activity describes how much influence a piece exerts, measured by the squares it controls, the targets it eyes and the freedom it has to move, so an active piece is worth more than its nominal value.
Piece coordination is the degree to which your pieces support one another and work toward the same target, so their combined force is greater than the sum of what each could do alone.
King safety is the degree to which a king is protected from attack, as determined by its pawn cover, the defenders nearby, the open lines pointing at it and how quickly the opponent can bring attackers to the area.
Center control means influencing the central squares d4, d5, e4 and e5, with pawns, pieces or both, so that your forces move freely and the opponent has less room to operate.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
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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.