What is a "Full Lit"?

It’s “full lid.” I’m not sure the origin, but it’s been use among press circles at least since the 90s. I’m assuming it refers to a container that us as full as possible before being closed.

I have never heard that term in any context other than the Ehite House Press Corps, nor can I find another reference to it. Can anyone else?

From the West Wing Glossary
“Full Lid
C.J. uses the phrase “full lid” to say that there will be no more news from the White House today. It is a real term used by the White House Press Secretary. Craig T. Fifer sent us a link to a transcript of a December 22, 1998 press conference given by Joe Lockhart (back when he was Press Secretary) where he says, “I can tell you, you have a full lid for Christmas Day.” ”