"Semi-Nomi" is a term that refers to a special sub-group of monsters. If a monster is a "Semi-Nomi Monster" then it means it must be [[Special Summon]]ed by its listed effect before it can be [[Special Summon]]ed by another effect. [[Aqua Spirit]], [[Harpie Lady Sisters]], and [[Black Luster Soldier - Envoy of the Beginning]] are all Semi-Nomi monsters. You can recognize a Semi-Nomi monster because it will have "This card cannot be Normal Summoned or Set. This card can only be Special Summoned by..." text in its card lore (although some cards, like [[Black Luster Soldier - Envoy of the Beginning]] do not have the first sentence, the 'No Normal Summon or Set' rule still applies). There is also a [[Special Summon Only Monster List|List of Semi-Nomi monsters]].