What does "position" mean in Texas Hold'em?

[uptrendfinancialsignal]

I just watched one strategy video and everybody kept shouting "position position position" like it's a secret code. I think I understand to some extent now but it still amazes me how sitting in one place can change everything. Before I got into poker I have always thought that cards alone mattered. But it turns out that timing is almost as important as the hand itself.