Can someone explain quality: max samples ?

[eddiemg]

Can someone explain how max samples works for the quality control on a technical level? I don't quite understand it. How does it render the image? What is one "sample"?

We're testing it, and it seems that it's not very consistent in terms of time it takes: we'll repeat the same sample count several times and get different time results, varying from 10 seconds to a minute for a render. And we're confused! Does increasing max sample, lets say from 100 to 200, double render quality and time to render?

Also, it seems it's faster when rendering individual still renders, say 1 minute for a still render, but when you do the animation of the same frame(s), it might take 2 minutes for each frame....any ideas on this?

Thanks!