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 or 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 books completely through in Finnish, and I couldn't find this por google with any palavras chave I could think of. xP

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

Thank you in advance. :)