What does "bocome an item" mean?

Posted by Charles Chen on December 05, 2001

I'm a Chinese in Beijing,and I'm crazy about English.When I read a trial report(Michigan v. Lesko: Husband Tried for Missing Woman's Murder) of www.courttv.com,I came across an expression which cannot be found in any dictionary.

In the case,the husband was accused of murdering his wife.When accounting some of the background information,the report says:
"Albert(husband) and Cindy(wife) met in the early 1980's. They quickly became an item and moved in together."

After searching using www.google.com,"become an item" seems quite popular.what does it (and "move in") mean.

thank you for your help