This might be a confusing term but essential to understand. 
The plan includes a pre-breakfast for 2 main reasons 

Food Frequency 

A pre-breakfast is like a mini snack, when the gap between waking and breakfast exceeds 2 hours. For example is you wake up at 5am but only have breakfast at 9 am, the pre-breakfast works as a mini snack. 

Insufficient Gap

If you do not have a large gap between waking and breakfast you can 

1. include the pre-breakfast as part of breakfast 

2. include it in any other meal of the day