WordPress at a glance
function is not described

wp_blacklist_check() WP 1.5.0

Does comment contain blacklisted characters or words.

Hooks in function
Return

true/false. True if comment contains blacklisted content, false if comment does not

Usage

wp_blacklist_check( $author, $email, $url, $comment, $user_ip, $user_agent );
$author(string) (required)
The author of the comment
$email(string) (required)
The email of the comment
$url(string) (required)
The url used in the comment
$comment(string) (required)
The comment content
$user_ip(string) (required)
The comment author's IP address
$user_agent(string) (required)
The author's browser user agent

Code of wp blacklist check: wp-includes/comment.php VER 5.0.3

<?php
function wp_blacklist_check($author, $email, $url, $comment, $user_ip, $user_agent) {
	/**
	 * Fires before the comment is tested for blacklisted characters or words.
	 *
	 * @since 1.5.0
	 *
	 * @param string $author     Comment author.
	 * @param string $email      Comment author's email.
	 * @param string $url        Comment author's URL.
	 * @param string $comment    Comment content.
	 * @param string $user_ip    Comment author's IP address.
	 * @param string $user_agent Comment author's browser user agent.
	 */
	do_action( 'wp_blacklist_check', $author, $email, $url, $comment, $user_ip, $user_agent );

	$mod_keys = trim( get_option('blacklist_keys') );
	if ( '' == $mod_keys )
		return false; // If moderation keys are empty

	// Ensure HTML tags are not being used to bypass the blacklist.
	$comment_without_html = wp_strip_all_tags( $comment );

	$words = explode("\n", $mod_keys );

	foreach ( (array) $words as $word ) {
		$word = trim($word);

		// Skip empty lines
		if ( empty($word) ) { continue; }

		// Do some escaping magic so that '#' chars in the
		// spam words don't break things:
		$word = preg_quote($word, '#');

		$pattern = "#$word#i";
		if (
			   preg_match($pattern, $author)
			|| preg_match($pattern, $email)
			|| preg_match($pattern, $url)
			|| preg_match($pattern, $comment)
			|| preg_match($pattern, $comment_without_html)
			|| preg_match($pattern, $user_ip)
			|| preg_match($pattern, $user_agent)
		 )
			return true;
	}
	return false;
}