Barista is a fancy euphemism for "dude who pours my coffee" (or dudette, no need to be sexist). A Barista is generally employed at a coffee house or one of the those mega international beverage conglomerates named after old Battlestar Galactica characters (you know what I'm talking about it). They specialize in whipping up some fancy overpriced coffees as well as espressos, lattes, etc. If they're really talented they'll even pour the cream on top in such a way that it makes a cute little heart design.
On Smallville, Lana Lang worked as a barista at The Talon theater and coffee shop. Martha Kent also worked there briefly to try and drum up a little extra money when times got tight.
On the CW Network TV version of The Flash, Iris West worked as a barista at a coffee house in Central City called CC Jitters. Another barista who worked at this establishment was a young blonde-haired woman named Tracy.