Plasma

Plasma is a nutrient-rich component of blood, including Sim blood. It is used by vampires in The Sims 3: Late Night and The Sims 4: Vampires to satisfy their thirst motive, which they have instead of hunger.

The Sims 3: Late Night
As stated in a Twitter session with Grant Rodiek, vampire Sims are also able to grow plasma fruits, which they can buy from the grocery store or at night in their own personal gardens. Vampires will also be able to eat plasma packs, which function the same as snacks for human Sims. A vampire can also raid the hospital for Plasma packs, or raid the grocery store for Plasma fruits.

If vampires have the Vegetarian trait, they are limited to only plasma fruit, instead of plasma from other Sims. If a regular Sim ingests any plasma product, they will become ill. Plasma packs are only available to Vampires, and regular Sims can't drink from Plasma packs.

The Sims 4: Vampires
Plasma, plasma packs, and plasma Fruits return in The Sims 4: Vampires. Plasma packs can be ordered on the computer by a Sim who has studied the vampire lore skill. Plasma packs can also be created from fish or frogs by Sims who have a high enough vampire lore skill; these packs will be of higher quality and quench more thirst. If a lot has the trait "registered vampire lair", Sims will occasionally receive plasma packs through the mailbox. Normal Sims can be asked for a drink, or compelled into letting the vampire bite them. If a Sim has purchased a certain vampire power point, they can "drain life spirit" from another Sim; this will provide the highest amount of plasma but the victim will pass out.

Trivia

 * Plasma packs and fruits are red in The Sims 3: Late Night, while they are purple in The Sims 4: Vampires.
 * Plasma Fruit plants are bushes in The Sims 3: Late Night, and trees in The Sims 4: Vampires.
 * It is presumed that Plasma is used instead of Blood in order to maintain a lower age-rating for the respective games.