The MOTD (Message of the Day) is a bit of description text that is displayed on the multiplayer list for users to see before they join a minecraft server. This text normally provides a bit of information related to the server, i.g Survival Hunger Games, Minigames Server 1.9+, Down for Maintenance, etc.
You can easily modify this text by accessing motd= vaule in the server.properties file and changing it to your preference in your hosting account.
In addition to simple text, you can also add colors and special colors to make it POP. If your looking to spice it up, consider using a Minecraft MOTD generator.
motd = Welcome to my New 1.9 Server
BACK TO SCHOOL SALE!
50% OFF for the first month on all servers with CODE: SCHOOL