The Catechism in Questions & Answers

79. How should human beings concern themselves with the invisible?

They should concern themselves with the invisible by turning to God and worshipping Him.
However, it is against the will of God to occupy oneself with the invisible in the form of necromancy or conjuring the dead (spiritism) (cf. Deuteronomy 18: 10 et seq.; 1 Samuel 28).

“There shall not be found among you anyone who [...] practises witchcraft, or a soothsayer, or one who interprets omens, or a sorcerer, or one who conjures spells, or a medium, or a spiritist, or one who calls up the dead. For all who do these things are an abomination to the Lord.”
Deuteronomy 18: 10-12

Practices of conjuring spirits, especially the spirits of deceased persons, are designated as “spiritism” (Latin spiritus = spirit).