There are a variety of words that can be used as synonyms for the phrase "billions of". Some of the most common options include "countless", "numerous", "incalculable", "innumerable", and "untold". Other choices might include "umpteen", "a multitude of", "myriad", "endless", and "vast". These synonyms can be used in a variety of contexts, from describing the number of stars in the sky to discussing the sheer volume of data generated online every day. Whether used in conversation, writing, or other forms of communication, these words can help convey the enormity of a given situation or object in an impactful way.