Western-style confectionery; Western sweets
Refers to cakes, pastries, cookies, and other sweets of Western origin, as opposed to traditional Japanese confectionery (和菓子).
This shop has delicious Western-style sweets.
I bought some Western-style confectionery on the way home for my birthday.
和菓子 refers to traditional Japanese sweets like mochi and dango, while 洋菓子 refers to Western-style sweets like cake and cookies.
Compound of 洋 (yō, 'Western') + 菓子 (kashi, 'confectionery'). The reading がし is a rendaku form of かし.