Custom Head meta tag

function theme_xyz_header_metadata() {
    
    // Post object if needed
    // global $post;
    
    // Page conditional if needed
    // if( is_page() ){}
    
  ?>
    
    <meta name="abc" content="xyz" />
    
  <?php
    
}
add_action( 'wp_head', 'theme_xyz_header_metadata' );