Short sleeve top. Two options, either a flat front/back, or slightly gathered front and back.
From the website: "Wear it tucked in to slouchy pants or a skirt, style it loose over jeans, or cinch it with a belt - the Aida is a wardrobe work horse. An Aida sewn up in a lightweight chambray or a Liberty lawn will become a handmade favorite. Make it with silk crepe de chine for work or an evening out. With two variations to choose from - flat front or slightly gathered bodice and back, you can pair the Aida with just about anything. The top is a quick sew - feel free to omit the buttonholes, as it can easily slip over the head."