From Yu-Gi-Oh!

Spell Cards (formerly known as Magic Cards until Magician's Force) are green-colored cards that have various effects to alter the play of the game. Often, a Spell Card has a single effect to provide a bonus to the user or a weakness to the opponent. All Spells are Spell Speed 1 (with the exception of Quick-Play Spells (Spell Speed 2). You may play as many Spell Cards as you would like per turn.

Although Spell Cards are often not as powerful as a Trap Card, they have the advantage that they may be played the turn they are drawn without having to Set them first. A Set Spell Card may be activated the turn it is Set as well (with the exception of Quick-Play Spell Cards).

In a typical Deck, Spell Cards occupy a little less than half of the total deck size (around 12-15 cards) and collectively with Trap Cards often have a 1:1 ratio to Monster Cards.

Some very powerful Spell Cards have been banned from tournament play, like "Raigeki". Konami has released new, less-powerful replacements for some of these cards. For instance, "Raigeki" has been replaced in Advanced Format by "Lightning Vortex", which requires a discard and only destroys face-up monsters, or "Flash of the Forbidden Spell" (whose card's title is indicative of a less-powerful replacement to "Raigeki"), which requires that all five of your opponent's monster card zones be filled with monsters in order to activate.

Used properly, a single Spell Card can significantly alter the game in the user's favour. It isn't uncommon for a player to win a Duel with the use of a single Spell Card. Snatch Steal is a common example of a Spell Card that is capable of winning a Duel.

The name Magic Card was likely changed to Spell Card to prevent confusion with the card game Magic: The Gathering, in addition to possible trademark disputes.

Types

A Spell Card's type is designated by a symbol to the right of the words "Spell Card". The various Spell Card Types are:

• Normal Spell: No Symbol, however some media give them a capital N symbol.
• Continuous Spell, symbolized with an "infinity" symbol.
• Equip Spell, symbolized with a "plus" symbol.
• Quick-Play Spell, symbolized with a lightning bolt.
• Field Spell, symbolized with a compass.
• Ritual Spell, symbolized with a torch.

From Yu-Gi-Oh Card Maker Wiki

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Spell Cards (formerly known as Magic Cards) are green-colored cards that have various effects to alter the play of the game. Often, a Spell Card has a single effect to provide a bonus to the user or a weakness to the opponent. All Spells are Spell Speed 1, with the exception of Quick-Play Spells, which are Spell Speed 2. You may play as many Spell Cards as you would like per turn.

Although Spell Cards are often not as powerful as a Trap Card, they have the advantage that they may be played the turn they're drawn without having to Set them first. A Set Spell Card may be activated the turn it is Set as well (with the exception of Quick-Play Spell Cards).

In a typical Deck, Spell Cards occupy a little less than half of the total deck size (around 12-15 cards) and collectively with Trap Cards often have a 1:1 ratio to Monster Cards.

Some very powerful Spell Cards have been banned from tournament play, like "Raigeki". Upper Deck has released new, less-powerful replacements for some of these cards. For instance, "Raigeki" has been replaced in Advanced Format by "Lightning Vortex", which requires a discard and only destroys face-up monsters.

Used properly, a single Spell Card can significantly alter the game in the user's favour.It isn't uncommon for a player to win a Duel with the use of a single Spell Card. "Snatch Steal" is a common example of a Spell Card that is capable of winning a Duel (though it has since been Forbidden).

Types

A Spell Card's type is designated by a symbol to the right of the words "Spell Card". The various Spell Card Types are:

• Normal Spell; No Symbol
• Continuous Spell, symbolized with an "infinity" symbol.
• Equip Spell, symbolized with a "plus" symbol.
• Quick-Play Spell, symbolized with a lightning bolt.
• Field Spell, symbolized with a compass.
• Ritual Spell, symbolized with a torch.

Example