More accurate than "returns the value of field x" would be "returns all values of field x" i.e.
$meta(x) returns all values of field x (e.g. $meta(artist)). If multiple values of that field exist, they are separated with ", ".
$meta_sep(x,sep) returns all values value of field x $meta_sep(artist,; ). If multiple values of that field exist, they are separated with sep.