top part of an apron; covering the chest
"The toddler pulled at his bib to wipe up a drop of tomato soup before it stained his shirt."
a napkin tied under the chin of a child while eating
"The toddler kicked his legs excitedly, sending crumbs flying off the colorful bib that was securely tied around his neck."
An item of clothing for people (especially babies) tied around their neck to protect their clothes from getting dirty when eating.
"My toddler spilled his milk all over his white shirt, so I quickly fastened a plastic bib around his neck before he could make a mess again."
Initialism of brought in by.
"The bib stands for Brought In By, which is why all the groceries were credited to John's account when he dropped them off at the door."