Type: Field (タイプ:フィールド, taipu: fīrudo) is a type of Magic cards introduced in BS49, but their prototype concept was introduced in BS19 with a cycle of Field-named cards, such as Flame Field. They're partially regular Magic cards, which at the end of their Main/Flash effect state they're placed on the Field upon resolving.
The On-Field effect is a passive effect which affects the player(s), and generally consists of anti-meta effects to counter specific decks or color mechanics, such as preventing deck discarding, unblockable attacks and anti-Grandwalker Nexus effects.
While usually unable to be affected by anything once on-field, effects such as The VenomKnight Blister, The RedRockKing Boanefel and The UnderworldExecutioner Carno can discard on-field Magic cards.
Like every "Type:" card, even if its effects are negated, it still possesses its type and can be targeted/counted for effects which require it.