What is back tension during the umbilical installation and service?

Backtension is usually described as the tension required to hold the umbilical during the lay operation.

If your umbilical is stored on a reel and is then being laid by a tensioner, you have 2 tensions;

1) the tension on the seaward side of the tensioner = the lay tension
2) a usually lower tension between the reel and the tensioner = the back tension

Thanks for the reply. Seems the back tension was used to define the installation load on the umbilical created by the tensioner.
My further question was that after the umbilical was laid on the seabed, some of them are taut or just 'sit' on the seabed without any tension? I heard it might be taut. When it was taut, there should be a tension in the umbilical, how to call this force and how big it was, how to detemine?
thanks again.