Over-Ear (cover the ear completely), on-ear (pressed against the ear), in-ear (inserted into the ear canal) or earbuds (inserted into the auricle, but not inserted into the ear canal).

The upper limit of the frequencies reproduced by the device. The human ear hears the standard frequency range: 20 Hz – 20000 Hz.

Bluetooth is a short-range wireless technology that allows you to connect headphones or portable speakers, a stereo system or a soundbar to your smartphone or laptop. For a certain version to work, both devices must support it. The versions differ in data transfer speed, power consumption, securing data transfer, anti-interference ability and range of connection.

To take advantage of a particular codec it must be supported by both devices

No higher than 32 Ohms for smartphone headphones. When using a good player or amplifier, it can be up to 100 Ohms. For stationary models you should coordinate the impedance with the amplifier power

It allows you to fold the headphones so that they take less space in your bag

Most of the headphones are dynamic but there are electrostatic, isodynamic, etc.

Open (with no insulation) or closed (passive noise insulation) or semi-open (intermediate version). Open headphones sound more airy and provide a wide stage, closed ones provide noise isolation and amplify low frequencies.

More sensitive headphones will play louder than headphones with less sensitivity (with the same signal level and resistance)

The material of earpads affects both your comfort and the sound. It can be leather, eco-leather, velour, fabric/microfiber and foam rubber.

Technology of increasing the standard USB voltage and current to speed up battery charging

The size of the driver membrane