It means to add to each individual card. Meta-tag data for each card is critical and I can tell you from all my efforts to go back through old cards and create better keywords, unique Card Titles and 'green light worthy' card descriptions (Artist Notes) for every card has truly made a huge difference in sales.
 
There are some great posts in the Artist Resource section you might find helpful:
 
https://gcucommunity.com/artist-resources/