It's a hard term to apply to cricket, especially with regards to batting.
I mean, in individual sports, something like tennis where a guy is serving can constitute choking, as they are in full control of the activity. Same with golf, where it's a stationary ball and you are in complete control when playing the shot, then it's much simpler to identify what people like to call a "choke".
Bowling a wide off the last ball, where only two is needed, that probably constitutes a choke. The game beforehand when Waugh got the runs, that's not a choke. The 2007 WC match against Australia, not a choke. It doesn't take much to make a mistake when on top, and giving your opponent a sniff; I think too often that gets referred to as choking. Even collapses, I don't think really come under choking; it's just plain chaos most of the time.
Where the Saffas come into the "choking" in that WC Semi is simply how they made the same mistake twice in two balls. They didn't have the composure to talk through what their plan was, there was still three balls left after that one to score one run.