Elgg database table names


In lots of elgg plugins I see queries like 

JOIN elgg_metastrings n on n_table.name_id = n.id 

JOIN elgg_metastrings v on n_table.value_id = v.id 

JOIN elgg_metastrings msn on n_table.name_id = msn.id


So as far as I understand, "v" "n_table" "n" "msn" are temporary tables. But I don't quite understand what do they represent. Is there a list of temporary table names which are used in elgg and what do they represent?