Caller ID is a feature that displays your phone number on the recipient's device when you make a call. Whether the number is sent depends on the caller's own settings, while whether it can be shown on screen depends on the receiving end. Mobile phones display incoming numbers as standard, but a landline needs a receiving-side subscription such as NTT East/West's Number Display to show them. Being able to check the caller's number before deciding whether to answer makes it a fundamental tool for nuisance call prevention.
Number notification is controlled using special codes. Dialing 184 before the phone number withholds your number, while 186 sends it. As a line-wide setting, you can choose whether your number is sent on every call, and the special codes override that setting for a single call. For example, to notify your number for a specific call from a line set to always-withhold, use 186.
A common misconception is that "notifying your number also shows your name to the recipient" - only the phone number is transmitted. Names appear only when the number is registered in the recipient's contacts or in a nuisance call database. With a phone number lookup app installed, business names and user reviews may display even for numbers not in contacts.
In business, displaying the company's main number is standard practice. By showing the company number rather than individual direct lines, return calls can be received at the main number. However, note that caller ID spoofing technology means displayed numbers are not always accurate. How far mechanisms for verifying the legitimacy of a caller's number (STIR/SHAKEN) have been deployed differs by country and carrier, so treat a displayed number as no proof of who is calling: look up the official contact yourself and call back. See how to handle anonymous calls for concrete steps when no number is shown.