I never considered the necessity of actually deleting a Yahoo account. I have created several over the years, and only use one daily and one or two others occasionally. But a friend asked today how to delete her Yahoo account, and I had to tell her I didn't think it was possible...

But it IS possible. Log into Yahoo then go here:
https://edit.yahoo.com/config/delete_user

Clicking that link won't delete your account -- you'll be asked to re-enter your password and click a confirmation button.

Now you know.