How to Correctly Use an Underscore: A Grammar Guide

I am back! Thank you for your patience while I was away taking care of everything in my life. I thought I’d launch 2020 with a post on how to correctly use an underscore since grammar blog posts are the most sought-after articles that I write on

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The underscore is one of the few punctuation marks with many names. Sometimes it’s called the understrike, the underbar, the underdash, the low dash, the low line. And way back in the day, it was called the underline.

Whatever you want to call it, the underscore looks like a dash that lives below the letters, like this:

_ See how the underscore resides beneath where letters exist on a line? _

While the use of the underscore has changed over the years, the purpose of the underscore today is to represent a space where a space is not allowed, from email addresses and usernames on the Internet to URLs and computer file names.

But before we dive into how you can correctly use an underscore, let’s explore how the underscore has changed in use over the years.

History of the Underscore

During the days of early word-processing technology, the underscore was a key character on a typewriter. It would take three steps for any typist to underline a word:

  1. Type the word that needs underlining
  2. Move the typewriter carriage back to the start of the word
  3. Overtype the word with the underscore to achieve an underline
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Thank goodness for computers! Now if we want to underline a word, we abandon the underscore key completely and click on the underline button in the menu bar.

Rumor has it that some word processing programs (none that I can seem to find) can automatically convert a word into an underlined word if formatted with an underscore before and after the word, like this: _underscore_

I, of course, cannot confirm this.

How to Type an Underscore

Today’s technology makes it easy to type an underscore. In fact, it’s only a two-step process that can happen in less than a second (if you’re skilled at typing):

How to use the slash correctly in a sentence
  1. Hold down the SHIFT key
  2. Press the hyphen/underscore key located to the right of the zero key on the number line of your keyboard

That’s it—you now have an underscore! But what are all the ways you can correctly use an underscore? Let’s explore all the ways you can apply this punctuation mark into your day-to-day practices.

How to Correctly Use an Underscore

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The purpose of an underscore, as stated earlier in this post, is to represent a space where a space cannot be applied. Even with the advancement of computer and Internet technology, some online or technical languages remain simplistic by not allowing an actual space to be applied in certain instances.

Hence the need for this punctuation mark! Here are the ways you can correctly use an underscore when on the computer or online.

Underscore in an Email Address or Username

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An underscore is often used in email addresses or usernames on the Internet in order to make them easier to read. That’s because when it comes to having a personal identifier online, spaces are not allowed. So, an underscore is used instead to show that space is needed.



Underscore in a URL

Like email addresses and usernames, spaces are not permitted in URLs. To designate space between words within a URL, you can apply an underscore where a space normally would appear.

In the earlier days of the Internet, underscore was the preferred method to addressing space within a URL. Today, the dash ( – ) is more often applied and recommended as a best practice. However, the underscore is still a valid way to represent space within a web address.

Underscore as a Computer File

Time to jump offline. To save a file back in the earlier days of computers, spaces were not allowed in the file name. This is still often the case for several computer programs today, so you’ll still receive file names filled with underscores.



Many programs today allow for spaces within the file names, so this isn’t as common of a way to correctly use an underscore in your daily life. However, if you still have old files on file, chances are there are underscores within the name.

Underscore as a Blank

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Just as the underscore was used back in the typewriter days to create an outline, the modern keyboard lets you create a fill-in-the-blank spot within a document by holding down the underscore key a few times without interruption. This is often applied to worksheets, contracts and forms.

Please sign here: _______________

I, _______________, agree to terms and conditions as stated above.

What is the state flower of Indiana? _______________

Did I miss one? How do you correctly use an underscore in your writing or daily life? Share in the comments section below.

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