"Gratis" comes form ancient Latin and means "free of charge" or "on the house" in English. The term is commonly used and understood in many different languages, although it's sometimes considered old-fashioned.
The Latin word "gratis" literally means "out of kindness," which indicates something is given free of charge without any request for a payment. Languages such as Italian, German, Dutch, Spanish and French commonly use the term in everyday speech. In the English speaking world, the word "gratis" is less common but generally understood. The term comes from late Middle English, a 15th Century version of the English language that borrowed a lot of terms from Latin, Italian and French.