The wp_nonce_field function that was used in this recipe is part of a security measure to ensure that the data being sent for submission comes from the WordPress administration pages and not an external source. By adding this function call, a hidden text field is added to the plugin configuration form with information that will be checked when the post data is received.

While it is optional, the first argument of the function is a unique identifier that should always be set to ensure better security. If it is not set, default values will be used, facilitating security breaches. The function also has a number of other optional parameters, as follows:

wp_nonce_field( [$action], [$name], [$referer], [$echo] );

The other three arguments are used to specify a name for the nonce, which would need to be matched on the receiving end, a Boolean variable to indicate if the referer field should be set for validation, and another Boolean parameter to determine whether the hidden form field should be displayed immediately or returned.