What describes a standard screwdriver?

A standard screwdriver is characterized by having a flat blade on one end, designed to fit into the straight, flat grooves of slotted screw heads. This straightforward design has been a staple in toolboxes, primarily because of its simplicity and reliability for driving and removing screws that feature a single straight slot. The flat blade allows for effective torque application, making it easier to both tighten and loosen screws.

The other types of screwdrivers mentioned in the options serve different purposes. A Phillips head screwdriver, for example, is specifically designed with a cross shape to fit into Phillips screws, providing more grip and reducing slippage. An adjustable screwdriver refers to those tools that come with interchangeable heads or the capability to change the blade's position, allowing for versatility but not fitting the traditional definition of a standard screwdriver. While screwdrivers can also be used to turn bolts in certain contexts, that is not the defining characteristic of a standard screwdriver; rather, it is the flat blade design that specifically identifies it.