Acknowledgement
Acknowledgement of service or defence. When you send your Employment Tribunal Claim Form (ET1) to the Employment Tribunal (ET), it is called "issuing proceedings". If you issue proceedings in the ET, you will receive an acknowledgement of claim confirming that your claim has been accepted by the ET. Your Employer will also receive an acknowledgement when they submit their defence to your claim.
See
The employment tribunal process
How to prepare your evidence for the employment tribunal
Layout of the employment tribunal hearing room
Layout of the employment appeal tribunal hearing room
How to complete the employment tribunal claim form
Application for a default judgment in the employment tribunal
How to write an effective witness statement for the employment tribunal
How to prepare your documents for the employment tribunal
Getting information from the other side (disclosure)