A sweater vest (known as a tank top, sleeveless sweater or sleeveless pullover in the UK) is an item of knitwear that is similar to a sweater, but without sleeves, usually with a low-cut neckline.
In the context of knitwear, a sweater vest is similar to a sweater but lacks armholes, typically characterized by a low-cut neckline and often referred to as a tank top or sleeveless pullover in the UK.