What is a fax machine? Fax meaning and how faxing works

What is a fax machine? It's a device that scans a paper page, sends it over a phone line as a stream of tones, and has another fax machine print an exact copy at the other end. "Fax" is short for facsimile, which means an exact copy - so a fax is a copy of a document sent over the phone.

Fax machines are less common today, but faxing isn't: doctors' offices, insurers, government agencies and law firms still ask for documents by fax. This guide explains the fax meaning, how a fax machine works step by step, what a fax number is, and how people send a fax today without owning a machine.

Fax meaning: what does fax stand for?

Fax comes from the word facsimile. Merriam-Webster gives "facsimile" as the meaning of fax, and defines a facsimile as an exact copy, and also as a system of sending and reproducing printed matter or pictures by signals over telephone lines.

So the word is used in three ways:

• A fax (noun) - the document that was sent: "I got your fax."
• To fax (verb) - to send a document this way: "Can you fax me the form?"
• A fax machine - the device that sends and receives faxes. People often shorten it to "the fax".

A fax is not an email or a scan you attach to a message. It's a phone call between two fax devices, and the pages travel during that call.

How does a fax machine work?

A fax machine is really three things in one box: a scanner, a modem that talks over the phone line, and a printer. Here's what happens when you send a page:

1. It scans the page. The machine reads the page line by line and turns it into black and white dots.
2. It dials the fax number. Like a phone, it calls the number you typed over a normal phone line.
3. The two machines agree on settings. The receiving fax answers, and the two exchange tones to agree on speed and page format. That's the screech you hear if you pick up a phone on a fax line.
4. It sends the pages. The dots are compressed and sent as tones, page by page. The receiver confirms each page as it arrives.
5. The other machine prints a copy. The receiving fax turns the tones back into dots and prints the page, or saves it as a file if it's a fax service.
6. Both sides get a result. The sender sees whether every page went through, often as a printed confirmation report.

This works between any two fax machines in the world because they follow the same international standards from the ITU: Recommendation T.4 sets the page format for "Group 3" fax machines (the kind in use today), and T.30 sets the procedure for sending a fax over the telephone network. The common fax modem standard, V.17, runs at up to 14,400 bits per second - which is why a page takes seconds, not a blink. More on that in how long a fax takes.

What is a fax number?

A fax number is a phone number that's answered by a fax machine or a fax service instead of a person. It looks exactly like any other phone number. When an office says "fax it to us", they give you this number, and your fax machine or fax app dials it.

You only need a fax number of your own if you want to receive faxes. To send one, all you need is the other side's number. How to get a fax number covers the options, from a landline to a number on your phone.

Why do people still use fax?

A fax goes straight from one device to another during a phone call, and the sender gets a clear result: delivered or not, and how many pages. Many offices built their paperwork around that years ago, and some forms are still accepted by fax and mail but not by email. The IRS, for example, lists fax numbers for forms like the SS-4 and Form 2848 - see IRS fax numbers by form.

Do you need a fax machine to send a fax?

No. The receiving office doesn't care what sent the fax - a machine, a computer or a phone. It just receives a normal fax. Today's options:

Faxing from your phone with HonestFax

1. Download HonestFax from the App Store.
2. Scan the pages with the camera, or add a PDF or a photo.
3. Type the fax number, check the price on screen, and tap Send.

HonestFax dials the number for you and shows each step - dialing, transmitting, delivered. If the line is busy it tries again, and if the fax fails in the end, the credits come back automatically. Your first page is free, a fax of up to 3 pages is $2.99, and credits never expire. To receive faxes, the 7-Day Pass gives you a US or Canadian fax number for a week. The full walkthrough is in how to fax from iPhone.

Have a fax machine in front of you instead? How to fax a document explains which side up and which buttons to press. And for every way to send without one, see how to fax without a fax machine.

Frequently asked questions

What is a fax machine used for? Sending and receiving copies of paper documents over a phone line - signed forms, medical records, prescriptions, tax forms and contracts are the most common.

What does fax mean? Fax is short for facsimile, an exact copy. A fax is a copy of a document sent over a phone line; to fax is to send one.

What does a fax number mean? It's a phone number answered by a fax machine or fax service. You dial it from a fax machine or a fax app, not from a regular phone call.

Is a fax the same as a scan or an email? No. A scan is just a picture of a page on your device. A fax sends that picture to a fax number over a phone call, and the other side gets it as a fax, not as an email.

Can I send a fax without a fax machine? Yes. A fax app on your phone or an online fax service sends a normal fax that any fax machine or fax service receives.

Checked on October 31, 2026: Merriam-Webster, "fax" ("The meaning of FAX is facsimile", by shortening and alteration) and "facsimile" ("an exact copy"; "a system of transmitting and reproducing printed matter or pictures by means of signals sent over telephone lines"). ITU (itu.int), Recommendation T.4 "Standardization of Group 3 facsimile terminals for document transmission", T.30 "Procedures for document facsimile transmission in the general switched telephone network" and V.17 "A 2-wire modem for facsimile applications with rates up to 14 400 bit/s" - all listed as in force. HonestFax prices as shown in the app on this date; the app always shows the price before you send.