http://www.techradar.com/news/what-does-enhanced-for-xbox-one-x-actually-mean-we-asked-microsoft

At Gamescom, Microsoft came out with a big claim; at launch there will be over 100 games enhanced for the Xbox One X. But with certain games like ReCore: Definitive Edition not being enhanced to full native 4K, it seems that there might be big differences in the quality of enhancements between games. 

When we asked for a definition of what exactly 'Xbox One X Enhanced' means,  Xbox's UK marketing manager Harvey Eagle said, “[Enhanced] means different things for different games. It’s really up to the developers to deploy the power of the console in whichever way they feel is right for their game.