While referring to the condition status of the nodes in Kubernetes, got confused with MemoryPressure and DiskPressure

This is the definition as per the docs : https://kubernetes.io/docs/concepts/architecture/nodes/

MemoryPressure  True if pressure exists on the node memory – that is, if the node memory is low; otherwise False

DiskPressure    True if pressure exists on the disk size – that is, if the disk capacity is low; otherwise False

OutOfDisk   True if there is insufficient free space on the node for adding new pods, otherwise False

Question here is, what is different in node memory and disk size for kubernetes?