What does "pretty quiet" mean in English for Spanish?

In English for Spanish, "pretty quiet" means:

bastante tranquilo/a

Listen to "pretty quiet": (If you have an HTML5 enabled browser, you can listen to the native audio below)

This is a phrase that is used in the GamesForLanguage English for Spanish Language Game in the following scenes:

• English for Spanish 4, Level 3, Scene 3