What's this charm called in english?

The one which makes the other person see a hallucination of whatever they are told they're supposed to see but the image can't be felt o heard and exists only as long as the person think it's real?

What is it called and what are the words to conjure it? I've only read the libri completely through in Finnish, and I couldn't find this da Google with any parole chiavi I could think of. xP

And for the matter... Does anyone know a good spell lista from which it'd be easy for someone like me to find the names and conjuring words for a specific spell? As in a lista that explains the spells throughly enough.

Thank te in advance. :)