Sentence:  Now conservation of <WSD>helicity</WSD> is maintained: the writhe of the loops in the second panel is compensated for by the opposite sign of the twist <WSD>helicity</WSD> along the loops. 
Meaning of the word marked with <WSD> tags:  Any of certain measures of the extent to which vortex lines (in fluid flow) or field lines (in a magnetic or electromagnetic field) kink and twist and/or link and coil around one another.