This is a white mesh chest binder (often just called a "binder"), which is a type of compression garment. It is sleeveless, tank-top style, and features a series of hook-and-eye closures down one side for adjustable fit. Binders are typically worn to flatten or minimize the appearance of the chest, commonly by transgender, non-binary, or gender non-conforming people. The mesh fabric suggests it is designed to be breathable.