That means that a player, who is on a team's 40 man roster, may not be moved to the minors without first clearing waivers.
MLB teams are limited on how many times they may move a player on their 40 man roster to the minors. Each time a team does this and the player spends at least 20 consecutive days in the minors, the team uses one of the player's 'options'. Only one option may be used per season so a team may move a player from the minors to the majors and back many times during a season with only one option being used.
A team has three options with a player. Once those three options have been used, the player is 'out of options' and must be placed on waivers and pass through without being claimed by another team to be moved to the minors.
MLB player Curtis Granderson throws right.
MLB player Adam LaRoche bats left.
MLB player Aaron Loup throws left.
MLB player Jose Ramirez can bat right or left (i.e. he is a switch hitter).
MLB player Brian McCann throws right.
MLB player Abraham Almonte throws right.
MLB player Bryan Holaday bats right.
MLB player Anthony Rizzo throws left.
MLB player Arquimedes Caminero bats right.
MLB player Brock Holt bats left.
MLB player Chris Archer throws right.
MLB player Corey Kluber throws right.