http://en.share-gate.com/blog/understand-sharepoint-crawled-and-managed-properties-for-search

1. Crawled properties are metadata (author , title , created etc)extracted from items while crawling SP content . Managed properties are created by devloper/administrator and are mapped to one or more crawled properties.2. Managed properties appear in refined search results and user can execute queries on these properties . Crawled properties can't be used for this.