Terms like "in the demo", "total viewers" and even the occasional "household rating" can be a little obscure when all you're trying to find out is how your favourite US show is doing. Here's a quick guide to what it all means.

Here's how we usually present ratings performance data on DS:

"Lost averaged 20m viewers and a 16% share in 18-49..."

The 20m viewers figure means that Lost averaged 20m viewers in total - that is, people age 2 and above - across its timeslot. Occasionally, if the data is available and it's relevant, we'll feature information on peak viewing figures - sometimes these can far exceed the average, for example if the Dancing With The Stars result overlaps with a popular show on another channel.

The other figure, 18-49 share, is often seen as the more important number. Adults 18-49 is the golden demographic for ad sales and the success or otherwise of a show in this demographic is often more important to buyers and, consequently, the TV networks, than the total viewers number. A "16% share in 18-49", therefore, means that of all people aged 18-49 watching TV while Lost was on, 16% of them were watching Lost.

Ratings data is copyright Nielsen Media Research.