A driver is software that lets an operating system communicate with a specific piece of hardware, translating general requests such as print this page into the exact commands that device understands.
In practice
When you plug in a USB microphone, Windows identifies it from the identifiers it reports and loads an audio class driver. That driver accepts sound samples from the device, packages them in a format Windows understands, and passes them to the recording app you open. Remove the driver and the microphone remains physically connected yet unusable by any program.
Common confusion
A driver is not the device's own internal software, which is called firmware, and it is not an ordinary application, even though makers often bundle a settings app with it. A single device can also rely on several drivers working together in layers rather than one monolithic file.
Why it matters to readers
Most questions about hardware behaviour in Windows eventually lead to which driver is serving a device, who published it and which version it is. Those three facts, visible in Device Manager, anchor any sensible comparison with reference release notes.
A closer look
Drivers also have lifecycles. A device bought years ago may still use the last package its maker released, while Windows continues to supply a class driver that keeps basic functions alive. Neither situation is unusual. What matters is that the driver in use matches the device, the Windows version and the system architecture, and that it came from a reference channel.
