Strategy is often defined as the "long-term" while tactic as the "short-term," especially in chess circles. But that definition is incorrect.
Tactics are not always short-term. In chess, it is possible to have a 20-move tactic– especially in an end-game. That's not "short" in terms of moves.
Strategies are not always long-term. In the Monty Hall problem, switching doors is the "best strategy" although it comprises just one step.
So what exactly is the difference between strategy and tactic?
Tactic is taking steps that result in a certain outcome (like TCP); strategy is doing the best against uncertainty (like UDP). In life, we try to do the best against uncertainty, which is why we don't always see a clear path to our destination, but still manage to get there.