Strategy in Chess
What is strategy in Chess? There are various definitions already available. One of the cutest is "Tactics is knowing what to do when there is something to do while Strategy is knowing what to do when there is nothing to do". I do not think that this definition is useful. The definitions which do not clearly distinguish between Tactics and Strategy are also not useful. In the following I propose my point of view.
Tactics regards the choice of moves using calculation so that the result is exactly known or knowable. Of course, one could commit mistakes but, for the sake of simplicity, such a case is disregarded here. For example, given a certain goal, tactics is that sequence of moves that achieves the task with absolute certainty. In a speculative way, if one could calculate all the variations leading to a win for white after 1) e4, this move would be a tactical move.
From such a point of view, Strategy is opposed to Tactics since it deals with situations of uncertainty (or, in mathematical terms, of probability). A strategical plan is implemented by choosing moves without having absolute certainty on the outcome, but using plausibility and educated guesses. For example, since the game of chess has not been mathematically solved yet, 1) e4 is a strategical move, steering the game toward certain type of positions.
Is any of this of any practical usefulness? Well, I adhere to the thought according to which "Chess is 99% Tactics". However, the remaining 1% is Strategy and it is going to make the difference against an equally skilled opponent. Knowing that Strategy has to do with chance and controlled risk might be a psichological incentive toward using more imagination in our games.