bottom gusset
Refers to the gusset (extra piece of fabric) inserted at the bottom of a bag or pouch to create depth and volume.
This tote bag has a wide bottom gusset, so it can hold a lot.
A pouch with a bottom gusset has more storage capacity than it looks.
Hiragana variant of the second element; less common than the katakana form.
Rare kanji form using 襠 for マチ; not commonly used.
Compound of 底 (そこ, 'bottom') and マチ ('gusset'), a term used in sewing and bag-making. The exact origin of マチ is uncertain, but it is commonly written in katakana in this context.