A headset is one headphone or pair with a built-in microphone. Headsets can be used for apps that require communication i.e. Skype, games with voice chat, mobile phones, etc.
These microphones are designed to filter out background noise from the desired sound. Especially useful in noisy environments.
More microphones result in better sound quality and enable the device to filter out background noise.
There is a control panel on the device body, so you can easily access the volume control or remote without having to interact with a cable or another device it's connected to.
The device has an option to mute/unmute a conversation directly from the device.
An accelerometer is a sensor used to measure the linear acceleration of a device. A common application is detecting when a device changes between vertical and horizontal positions.