Hi! I am very confused about the phrase' common thread' in the following sentence. What is the exact meaning of common thread? If you don't mind,can you also please explain the words in Italics? Storing trillions of bits of information and working with Geographic Information System(GIS) , the system uses geogrpahic position as a common thread. Although it became popular in the 1990s, GISs were developed in 1960s.