Trading strategy: A trading strategy defines precisely how you should enter and exit trades. For example, "Buy Bitcoin when it drops below $10000, sell when it reaches $12000" would be a very simple trading strategy.

Trading plan: A trading plan is a comprehensive blueprint covering everything from your goals, motivation, and attitude to risk, through to risk management rules and analysis of past trades. It can (and should) include both your strategies and your commitment to keeping a diary.

Trading Diary: A trading diary is a written record of everything that happens when you trade, including entry and exit points, profit/loss, trading statistics, and even your emotional state before, during, and after each trade.

The trading strategy is a very specific plan that the trader follows, including entry and exit points and certain instructions that are set.

The trading plan is a bit more broad than the strategy in the sense that it also incorporates aspects such as the trader's main aims, risk management, and this needs to be viewed in conjuncntion with the strategy,

The trading diary supplements the former two as the trader will keep track of his transactions so that he can refer to them and see what he did, where he did well, where he could have done better etc.