"String up" generally means to suspend or hang something by tying it with string or rope. It can refer to hanging objects for display or storage, such as stringing up lights for a festive occasion or hanging clothes on a clothesline. In a more figurative sense, "string up" can also mean to execute or punish someone by hanging, historically used in contexts of vigilante justice or mob rule. However, in contemporary usage, it more commonly refers to the act of suspending something in a literal, non-threatening manner, such as stringing up decorations or organizing items for storage.