Refers specifically to the toilet fixture itself, as opposed to a squat toilet (和式便器). Often used in product descriptions or when discussing bathroom fixtures.
See also: 洋式トイレ
Western-style toilets are becoming more common in public restrooms these days.
和式便器 is a squat toilet, while 洋式便器 is a Western-style sitting toilet.
洋式トイレ refers to a Western-style toilet room or stall, whereas 洋式便器 refers specifically to the toilet bowl itself.
Compound of 洋式 (Western-style) and 便器 (toilet bowl).