It is a new type of report, which is made by PageSpeed Insights. Now the web page speed suggestions are integrated in Google Analytics under Site Speed.
Here is one sample report of one of my webpage here. It gave me two suggestions, including Desktop and Mobile.
In the report, it shows score of Desktop is 76 out of 100. It is medium score. The minimum score is 75 for me.
Click the title of these two suggestion, it will expend and show me which parts are needed to be optimized.