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 Jīnhuá huǒtuǐ) or generic ham.
方腿 specifically signals the cheap pressed-loaf style.