Interesting question! I would suggest the food that you eat is irrelevant in defining a meal but that the time at which you eat in relation to your lifestyle is what determines the nature of the meal.
For example, if you work a regular 9 to 5 job and sleep from 11pm to 7am, whatever you eat at 8am is your breakfast. In a literal sense, you are breaking the fast in which you have indulged while sleeping. Conversely, if you work 11pm to 7am and sleep 1pm to 9pm, a meal at 10pm would be your breakfast.
The way I see it is that all other meals are defined in relation to the time at which you eat breakfast.
Hope this makes sense! :)