This is an exponentially weighted moving average with smoothing constant 0.1. It shows the overall trend of your data, but lagged. If most of your daily numbers are below this trend line then you are inexorably dragging it down.
For the case of weight loss, this is another way -- proposed in The Hacker's Diet
-- to see the forest through the trees, to see past the daily random fluctuations to what your weight is really doing.