dT
Time
The Delta Time
node returns the change of time between two world updates, specifically the time between the current update and the one before.
This Unity Documentation about Delta Time may be relevant in helping understand what this does. And following that, this has an excellent explanation about Time Frame Management, which in general may help with working with this node in your content.
Uses
Using this node, you can make an accumulator or a timer using the frames here and storing them to a variable and adding them every frame.
Outputs
* (float)
The difference in time between this frame and the last frame.