G4 means "pause for a given duration of time".
The command is used as such :
Which means : pause for 5 seconds.
This is useful for example to wait for spindles to ramp up to speed, or to wait for small layers to cool down on 3D printers.
|S||Duration to wait in seconds||G4 S10|
|P||Duration to wait in milliseconds ( thousandth of a second )||G4 P100|
Note that if grbl_mode is set to true then the P parameter is the duration to wait in seconds, not milliseconds, as a float value. This is to conform to G-Code standards.
These resources are used as references for Gcode :