Managed Properties in SharePoint 2013

<object height="1" id="plugin0" style=";z-index:1000;" type="application/x-dgnria" width="1"><param name="tabId" value="{297A97BB-5574-451E-A1C1-551AD44BDBFF}" /></object>

OK - so I've read what I can find on the "Searchable" vs. "Retreivable" configuration choices in a Managed Property in SharePoint 2013.  Color me clueless, but I"m not getting it.  I don't see a clear difference between the two nor do I see a use case scenario that would help me differentiate between them.

Any help is appreciated.

TIA.

---

Bill English