RAM (Random Access Memory) is a computer’s short-term data storage, where the data that the server is currently using is stored. In case of Minecraft servers, it is used to store information about your Minecraft world and players. The higher RAM means the higher storage for your server to store information.
How much RAM do I need?
We would recommend you to settle with around 3-4 GB for your minimal configured Minecraft server (SMP). 6+ GB RAM would be only advisable in case of high amount of players or/and complex server configuration.
NOTE! High amount of RAM is not always good for your server since it could be mostly eaten by memory leaks (poor coded plugins) for no extra benefit.