Isn't this simply the error that is given here? What I mean is that 5.5336(2) corresponds to 5.5336 +/- 0.0002.

Isn't this simply the error that is given here? What I mean is that 5.5336(2) corresponds to 5.5336 +/- 0.0002.

This is the uncertainty in the last digit. If you are using any computer program for Rietveld refinement then it will give you this delta/uncertainty in the cell parameters as well.

This is the uncertainity in the last digit as already mentioned by Dr. Ulrich and Dr. Falak Sher. It corresponds to the last digit i.e. +/- 0.0002 in your question. Good luck!