The audio tag is used for questions involving speakers, microphones, connections between them and computers, and applications for dealing with it.
This can involve the digital transmission of sound and its conversion into analog signals which are then amplified so the listener can hear them through loudspeakers. Conversely, it also involves the recording of acoustic sound via microphones, and the analog audio signal's conversion into digital format so that it can be recorded and manipulated by a computing device. Finally, the tag "audio" will also be used to refer to the digital manipulation and signal processing of sound materials in applications (such as the Digital Audio Workstation).
The "all-in-one" 3.5 mm headphone/microphone jack
Any modern Apple devices (MacBook, iPhone, and iPad) that still include a 3.5 mm audio jack can handle both headphones and a microphone simultaneously. The most common way to do this is with Apple's wired EarPods with the 3.5 mm connector. This connector is a backward-compatible improvement over the original tip-ring-sleeve (TRS) connector that required two ports in order to use headphones and microphone at the same time. The original TRS connector has 3 poles, and the new all-in-one connector has 4 poles. The extra pole is used to carry the microphone signal. For more detail, check out this answer about using microphone input on a MacBook Pro.