Harmony

Harmony is a Monk passive skill, unlocked at level 45. In patch 2.1, it replaced One with Everything (see below).

In-game
The 40% conversion means that an item that has +160 Fire resistance will instead grant 64 all resistances and additional 96 Fire resistance, to a total of 160 Fire resistance and 64 to all other elements (including Physical).

Development
Prior to patch 2.1, this skill was named One with Everything: it was making the resistances to all seven elements always equal to the highest resistance the Monk had (i.e. if the highest resistance was Fire with 2100, all other resistances would be escalated to 2100). It was the most used of the Monk's skills: with properly assembled gear (all resistances + same element resistance on each piece) it effectively increased all resistances by +160%. However, developers felt that this was making the skill look mandatory and undermining the build diversity, and so eventually replaced OwE with Harmony.