Catechism of the Catholic Church §2729 — excerpt
The habitual difficulty in prayer is distraction. It can affect words and their meaning in vocal prayer; it can concern, more profoundly, him to whom we are praying, in vocal prayer (liturgical or personal), meditation, and contemplative prayer.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.