A "Required Field" is a field that must be filled in with value before submission of a form. Required field sometimes known as Mandatory field or Compulsory field.
As of writing, only Opera and Firefox support "Required" attribute of input textbox. Please see table below.
To make a field as required field is fairly simple, you are only required to add a "required" boolean attribute into your input element.
<label for="movie">What is your favorite movie : </label>
<input name="movie" type="text" required />
<input type="submit" value="Submit"/>
The picture below shows us how Firefox and Opera prompt user to fill in value if a "Required field" is left blank upon submission.
Below is the demo of "Required field", feel free to test it with your browser.