It appears to stand for either Turbofan Power Ratio or Turbine Pressure Ratio depending on where it's found.
I think it's going to be Turbofan Power Ratio on the 787.
From what I've read on the net, it appears to basically display thrust as a percentage of maximum available in each mode ie TO, CLB, GA, and can even be used in reverse.
So you can now set say 85% of Take off power or Climb power or have 85% reverse thrust and the TPR will read 85.
Looks like it'll be possible to takeoff with 100%TPR get airborne call for "climb thrust" and still have 100%TPR but now in CLB thrust mode, CLB 1 will always be 90% and CLB 2 80% initially until it is blended out towards 100% again during the climb.
Somewhere in the change from TO to CLB the TPR will have to read either less than 100% TO or greater than 100% CLB though. Probably greater that 100% climb, at least it'll appear correctly as reducing thrust towards 100% climb thrust.