A social media wall is a live or aggregated feed of social media content from social media platforms displayed on any digital signage display. It can be Tweet walls, Instagram posts walls, Facebook walls, or a combination of all networks in one place. On the other hand, social media feeds are widgets generated by social media aggregators that contain content from various social media accounts and are shown on a website.  But please note that these differences are very small, so we usually use social media feeds and social media walls as synonyms.