It means he is on the minor league, not major league, roster, but still invited to major league Spring Training. Normally players on the major league (40-man) roster report to the major league camp and players with minor-league contracts report to the minor league camp. However, veterans signed to minor league contracts and some prospects are sometimes invited to major league camp even though they're not on the major league roster. If they actually make the team for Opening Day, then they have to be added to the major league roster.