A bit of fat pork or bacon used in larding.

diced and fried bacon

a small strip of pork fat or a cube of cooked bacon used as an ingredient or garnish.

a strip of bacon or pork used to lard meat.

A lardon is a piece of bacon taken from the rendered back fat of a pig. Unlike the slices of bacon ubiquitous in most of the English-speaking world, lardons are cuboids roughly 1 cm×1 cm×2 cm. This is the most common form of bacon sold in much of Europe, but is something of a gourmet ingredient in the United States.