A 3.5mm jack is a small audio connector commonly used for headphones and speakers. It allows you to plug in devices like smartphones, tablets, and laptops to listen to music or make calls. The size of the jack is 3.5 millimeters in diameter, which is why it’s called a 3.5mm jack. These jacks are versatile and can carry both audio and microphone signals, making them popular for headsets as well. While many devices still use this standard, some newer models are moving towards wireless options, but the 3.5mm jack remains a reliable choice for many users.