WordPress at a glance
filter is not described

excerpt_length filter-hook . WP 2.7.0

Filters the number of words in an excerpt.

Usage

add_filter( 'excerpt_length', 'filter_function_name_6900' );
function filter_function_name_6900( $number ){
	// filter...

	return $number;
}
$number(int)
The number of words.
Default: 55

Where the hook is called

wp_trim_excerpt()
excerpt_length
wp-includes/formatting.php 3324
$excerpt_length = apply_filters( 'excerpt_length', 55 );

Where the hook is used (in WP core)

Does not used.