Semi-Nomi

(Taken from Yu-gi-oh wiki)

"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 Summoned by its listed effect before it can be Special Summoned by another effect. "", "", and "" 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..." in its text (although some cards, like "", do not have the first sentence, the "No Normal Summon or Set" rule still applies).

After a Semi-Nomi monster has been Special Summoned, it can be Special Summoned through other effects. This only lasts as long as the Semi-Nomi monster does not return to the Hand or Deck. As long as the Semi-Nomi monster remains on the field, in the Graveyard, or removed from play, you can Special Summon it again with other card effects.

There is also a sub-type of monsters called "Nomi".