As a non-native english speaker my search for recipes has lead me wondering what the hell is a “spanish onion” as some recipes call for. my understanding from googling is that it is a special variety of the basic yellow onion kind of like varieties like san marzano are for tomatoes or just another name for the ‘basic yellow onion.’
I think Spanish onions are just a varietal of onions, like Vidalia onions. They are a kind of sweet onion - basically a yellow onion grown in low-sulfur soil so it doesn’t have that pungency and is thus “sweet”.