Okay kiddo, so a long time ago, people used to read and sing from books called psalters. Psalters were special books that had the sacred songs and prayers of the Bible in them.
Now, some people in Europe would write these psalters in a special language called Latin. Latin was a language that a lot of people used to speak and write in a long, long time ago.
These Latin psalters were very important to people because they helped them pray and worship. They were often very beautifully written and decorated with fancy pictures and designs.
People would often carry their Latin psalters with them and use them during church services or even at home when they wanted to pray.
Even though not everyone could read Latin, people still loved the psalters because they could look at the pretty pictures and follow along while others read or sang from them.
So that's what a Latin psalter is, a special book full of songs and prayers in an old language that people used a long time ago to worship and pray.