Average Price Difference is the weighted average of the price differences between your prices and the market prices. For instance, '-3.4%' means your prices are, on average, 3.4% below the market. The Weighted Price Difference is useful as an indicator at-a-glance of your positioning vis-à-vis the market. If you see that number change significantly, you should take a deeper look into your competition, to find the most important price changes and adjust yourself accordingly.
Average Position shows the average percentage of competitors below your prices. For instance, 53% indicates out of 100 sellers, 53 have cheaper prices than you (and therefore, 47 are more expensive). The Average Position provides an instantaneous indication of your competitiveness. Keep an eye on it to ensure your positioning remains stable.
% of Sub-Optimal Prices is the percentages of your prices which are not at a proven, psychological level. You should wether raise them to the next psychological level, which will result in higher margins while keeping approximately the same volume, or lower them to the previous psychological level, which should yield significantly more sales. Look for the 'warning' indicator in your Products list, it will give your price hints.
Direct Competitors is the number of direct competitors automatically identified by the system, based on the similarity of your catalogue and theirs.