Pressed ham: pork, often finely minced, moulded into a rectangular block and cooked, sold whole or sliced in plastic film. It is ready to eat and mostly sliced cold for sandwiches.
There are a few slices of square ham in the sandwich.
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Literally 'square leg' - a processed-meat product pressed into a rectangular block, sliced for sandwiches and bento. Distinct from 火腿 (huǒtuǐ, 'fire-leg') which can mean either traditional dry-cured ham (e.g. 金华火腿) or generic ham. 方腿 specifically signals the cheap pressed-loaf style.