What is ;Leverage Browser Caching? ; Thanks in advance
Federico Sasso: It's a recommendation for building faster web sites.
Basically, it just means what it says: it recommends to make good use of the browser cache so that next time the same user requests the page, he/she will find part of the contents already downloaded locally and will load the page much faster, not having to request them again to the server.
You probably come across it using the tool Google PageSpeed. It must be linked to an help page from there.