escaping an ampersand

When using the W3 validator, I get this error:

‘&copy 2007 Atticus Publishing, Inc.      

If you meant to include an entity that starts with “&”, then you should terminate it with “;”. Another reason for this error message is that you inadvertently created an entity by failing to escape an “&” character just before this text.’

okay so I changed it to © – my bad. but what does it mean by escaping the ampersand (&) ??? I tried forward/backslash and it just shows up inline as text… what does this mean?