What is Latin?
Latin is a dead language, originally from Italy. It is the ancestor of so called Latin languages, such as Italian, French and Spanish. It had a major influence on English too.
Now it is used only for religious reason by Catholics. People study it also if they are interested in ancient coltures.
Here's a brief history of Latin:
In very ancient times Latin was the main language spoken in central Italy, with several local variations (technically speaking pre-Roman variants of Latin are called italic languages, but that's not important). It was also spoken also in Rome
When Rome begun becoming a powerful city, the Romans started exporting their language. By 300 BC Latin was spoken in all Italy.
With the expansion of the Roman empire, around 1st century BC-1st century AD, Latin was exported as an administrative language in much of Europe (today it would be Spain, France, Greece, Britain and Yugoslavia) in part of the Middle east (today it would be Turkey, Israel, Tunisia and Egypt).
When the Roman empire collapsed, places where Lain was very prominent developed their own languages, with a strong Latin-derived structure: Spanish, French, Portaguese... That's why people who speak Spanish sometimes are called Latin.
English was very mildly influenced by Latin at first, but then it imported a lot of Latin-derived words after the French conquest.
Italy was a little peculiar, as people spoke Italian but Latin remained the main written language until about 1200 AD (when Dante wrote the Divine Comedy) and sometimes later. Galileo Galilei (who lived in the 1600s) wrote mostly in Latin.
Catholics kept praying mainly in Latin until the 1960s, when the Vatican decided it was time to move on and use modern languages. But some still keep Latin as a religious language.