an explanation that can be understood by someone who doesn't know much about the field being discussed. Layman's terms would explain any jargon words and probably have to go through a lot of background information a person who knew the subject would not need to hear.

When trying to explain something to someone who isn't being very receptive, I often roll my eyes and say

"Ok, in layman's terms..."

...and re-explain it, hoping to get the listener on the ball.

When used properly, its quite an effective insult, making the person you're talking to look like a complete ass.