John Lightfoot on John 6:12

[The fragments that remain.] It was a custom and rule, that when they ate together, they should leave something to those that served: which remnant was called peah. And it is remarked upon R. Joshua, that, upon a journey, having something provided for him by a hospitable widow, he ate all up, and left nothing to her that ministered. Where the Gloss: "Every one leaves a little portion in the dish, and gives it to those that serve; which is called the servitor's part."

Although I would not confound the fragments that remain with the peah, nor would affirm that what was left was in observation of this rule and custom; yet we may observe, that the twelve baskets full of fragments left at this time answered to the number of the twelve apostles that ministered. It is otherwise elsewhere.