Full forms: mobile and telecom

27 full forms, each with a line on what it means.

These are the short forms printed on SIM packs, phone boxes, recharge plans and telephone bills, and the ones that appear in your phone's settings. Knowing them is practical. If you know that an OTP is a one time password meant only for you, a fraudster's call asking for it sounds wrong at once. If you know the IMEI is the identity of your handset, you know what to give the police and your operator when a phone is lost. The page also covers the generations of mobile networks, radio terms and the older telephone words, STD, ISD and PCO, that still appear in general knowledge papers.

Explained in full: OTP SIM GPS

• SIM

  Subscriber Identity Module

  The small card, or built-in chip, that identifies your mobile connection to the network.

  SIM explained Copy

• eSIM

  Embedded Subscriber Identity Module

  A SIM built into the phone that is set up by software, with no card to insert.

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• SMS

  Short Message Service

  The ordinary text message service of mobile phones.

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• MMS

  Multimedia Messaging Service

  A message service that can carry pictures and sound over the mobile network.

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• OTP

  One Time Password

  A code sent to your phone or email that works only once, used to confirm a login or payment. Never share it.

  OTP explained Copy

• GSM

  Global System for Mobile Communications

  The mobile phone standard used by most of the world for second-generation networks.

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• CDMA

  Code Division Multiple Access

  A mobile network technology that was an alternative to GSM.

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• LTE

  Long Term Evolution

  The technology behind 4G mobile networks.

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• VoLTE

  Voice over LTE

  Phone calls carried over the 4G data network, giving clearer sound.

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• 5G

  Fifth Generation

  The fifth generation of mobile network technology, faster than 4G.

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• IMEI

  International Mobile Equipment Identity

  The unique 15-digit number of a phone handset. Dial *#06# to see it.

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• GPS

  Global Positioning System

  The satellite system of the United States that lets a device find its position anywhere on Earth.

  GPS explained Copy

• NavIC

  Navigation with Indian Constellation

  India's own regional satellite navigation system, run by ISRO.

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• STD

  Subscriber Trunk Dialling

  Direct dialling of long-distance calls within the country, using an area code.

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• ISD

  International Subscriber Dialling

  Direct dialling of calls to other countries, using a country code.

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• PCO

  Public Call Office

  A booth or shop with a public telephone, once common across India.

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• TRAI

  Telecom Regulatory Authority of India

  The regulator of telephone, internet and broadcasting services in India.

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• DND

  Do Not Disturb

  A setting or registration that blocks unwanted calls, messages or notifications.

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• USSD

  Unstructured Supplementary Service Data

  The system behind short codes such as *123#, which work without internet.

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• NFC

  Near Field Communication

  Very short-range wireless used for tap-to-pay cards and phones.

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• BSNL

  Bharat Sanchar Nigam Limited

  The government-owned telecom company of India.

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• DTH

  Direct to Home

  Television delivered straight from a satellite to a small dish at the viewer's home.

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• FM

  Frequency Modulation

  A way of sending sound by radio that gives clear reception; FM radio uses it.

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• AM

  Amplitude Modulation

  An older way of sending sound by radio. In clock time, AM means ante meridiem.

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• PIN

  Personal Identification Number

  A secret number for a card, phone or account. In Indian addresses, PIN means Postal Index Number.

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• APK

  Android Package Kit

  The file format of an Android app. Install apps only from trusted stores.

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• App

  Application

  A program for a phone or computer. A short form, not an abbreviation of several words.

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How to read an entry

The letters in bold are the short form as it is normally written. Under it is the full form, and then a line of meaning in plain words. Where the same letters mean something else in another field, the entry mentions it. "Copy" puts the short form, the full form and the meaning on your clipboard, ready to paste into notes or a message.

Check what matters. These pages explain names and terms in general. Rules, dates, fees and limits change: take them from the official body. Read on 12 November 2026.

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