When people say they are "creed," they are reciting the Creed—the statement of faith that says "I believe in the Father, and in the Son, and in the Holy Spirit." This is the Creed most commonly recited by Christians. However, the Creed has many different versions and interpretations.
The Assassin's Creed games are set on a world populated by dozens of different languages. Some, like English, are based on the languages of the real world, while others have been created by the game's designers. Each language is different and has its own unique alphabet. Some have been around for millennia while others are still being created.
Some of the most interesting languages in Assassin's Creed are those that don't exist in the real world. These are known as planar languages. These are extremely difficult to learn because they require a special Tongue to interpret. They are also usually spoken by powerful magic users and cannot be heard by mortals without their aid.
One such planar language is virras, which is used by the Viashino and can be heard as hisses, growls, and low-pitched murmurs. Virras has a written form as well, using a mixture of pictographs and a consonant-based logographic system.
Another planar language is azurit, which is used by the Isu. The Isu are a god-like race that, according to Assassin's Creed lore, predate human civilization. In order to understand the Isu, a special Animus called Valhalla was built to act as a Rosetta Stone, helping decode the complex language that the Isu spoke.