Velocity user-guide Quiet Reference Notation
When Velocity encounters an undefined reference, its normal behavior is to output the image of the reference. For example, suppose the following reference appears as part of a VTL template.

<input type="text" name="email" value="$email"/>

When the form initially loads, the variable reference $email has no value, but you prefer a blank text field to one with a value of "$email". Using the quiet reference notation circumvents Velocity's normal behavior; instead of using $email in the VTL you would use $!email. So the above example would look like the following:

<input type="text" name="email" value="$!email"/>

Now when the form is initially loaded and $email still has no value, an empty string will be output instead of "$email".

Formal and quiet reference notation can be used together, as demonstrated below.

<input type="text" name="email" value="$!{email}"/>