Timing pertains to the relationship between the hitter's movements during their gather, stride, and swing and the pitcher's movements during the delivery. Timing is important because, no matter how good your mechanics are or how quick your swing is, if your timing isn't solid then you won't be able to hit the ball well.
Andres Torres struggles during 2012 forced me to understand how Timing in baseball hitters works, which paid off for Mark Trumbo in 2016.
I discuss Timing in this related essay...
Timing
Many people have speculated about why Jose Bautista's career suddenly took off in 2010.
In my opinion, it wasn't due to steroids and it's only partly due to the fact that Bautista adopted more of a Yes, Yes, No approach to swinging. I believe the bigger answer to the question of why Jose Bautista has been so successful of late comes down to his Timing and what he starts talking about at the 1:03 point of this clip...