Talk:Toroid/@comment-189.127.239.54-20190119030725/@comment-2601:601:CE7F:CE6B:5808:C5C3:6816:237-20190119230612

Toroidal inductors and transformers are inductors and transformers which use magnetic cores with a toroidal (ring or donut) shape. They are passive electronic components, consisting of a circular ring or donut shaped magnetic core of ferromagnetic material such as laminated iron, iron powder, or ferrite, around which wire is wound.

As far as I know, they're used in power transformers and the like, and generate large magnetic fields.