Copyleft and Share-Alike are two very similar types of licences. Here is how Wikipedia defines them:
Copyleft (a play of the word copyright) is the practice of offering people the right to freely distribute copies and modified versions of a work with the stipulation that the same rights be preserved in derivative works down the line. (Source)
Share-alike is a copyright licensing term, originally used by the Creative Commons project, to describe works or licences that require copies or adaptations of the work to be released under the same or similar licence as the original. Copyleft licences are free content or free software licences with a share-alike condition. (Source)
Are there any meaningful distinctions between these concepts, or is the only real difference their heritage and most common uses (software vs media)?