I would like to confirm if the shutter lag is a loss that is only suffered for the first frame in Burst-mode. Is this correct?
I had the impression it was an indication of how slow the the shutter travels between each exposure of the sensor.
Assuming your question is in the context of a multi shot burst taken by holding down the shutter button, technically speaking shutter lag would apply only to the first frame and not each subsequent frame only if you have the camera set to take all of the photos in the burst without re-metering or refocusing between each frame. Even then there is an additional consideration for the second frame and following: the amount of time it takes to readout the sensor and recock the shutter curtains following the end of the previous exposure. So it can be a mixed bag - you don't have to wait for AF or metering after the first shot but you do have to wait for readout and recocking.
Shutter lag is more or less defined as the amount of time between when the shutter button is fully pressed and the first curtain begins to open to expose the sensor. Anything that occurs during that interval is included in "shutter lag": metering, focusing, etc. Some testers will publish a figure for shutter lag measured when the camera was prefocused on the subject and exposure was set manually as well as the more typical figure for when the camera must meter and focus after the shutter button is pressed.