What does it mean when they say the universe is expanding?

Where is the edge of the universe? Science Questions with Surprising Answers

What Redshift Reveals About an Object

STTGL Vs What if Ultron - Battles - Comic Vine

Our universe is actually 27 billion years old, almost double the current age estimate •

Who Will Have the Last Word on the Universe? - The New York Times

What is the universe expanding into?

Our expanding universe: Age, history & other facts

New supernova data could help reveal how fast the universe is expanding

Expansion of the universe - Wikipedia

What does it mean when we say space is expanding? - Quora

How do we know the universe is flat? Discovering the topology of the universe