It's just the idea that you benefit from timed nutrition around training.
Bodybuilders used to go on about the "anabolic window" and urgently chug down a protein and glucose shake before they left the gym. Turns out that's mostly bullshit but not entirely.
The main thing is to ensure you're getting enough protein and other nutrients over the course of the day and the timing isn't all that important. However it is important if you're working out several times a day as you'd need to replenish your glycogen before your next workout or feel tired. It also appears that there is some benefit to ensuring you've adequate protein in the system whilst training and afterwards. Not a huge difference but, depending which studies you look at, a worthwhile one. So the general advice is to have a meal containing protein and carbs before training (e.g. an hour or so before) and one directly afterwards (exact times won't matter since your pre-working meal will still be in effect). You won't go far wrong if you shoot for 30-50g of protein and carbs for a pre and post workout meal. That could be a shake or a proper meal depending.
