WordPress at a glance
filter is not described

posts_where filter-hook . WP 1.5.0

Filters the WHERE clause of the query.

Usage

add_filter( 'posts_where', 'filter_function_name_4635', 10, 2 );
function filter_function_name_4635( $where, $this ){
	// filter...

	return $where;
}
$where(string)
The WHERE clause of the query.
$this(WP_Query)
The WP_Query instance (passed by reference).

Where the hook is called

WP_Query::get_posts()
posts_where
wp-includes/class-wp-query.php 2376
$where = apply_filters_ref_array( 'posts_where', array( $where, &$this ) );

Where the hook is used (in WP core)

Does not used.