A switchback is when a trail zig-zags (reverses direction multiple times times) to reduce the slope or grade of the path up/down a hill/slope.
Here’s an example:

Rerouting it is just changing the location of the trail. This is done when an older trail has irreparable damage or was poorly designed leading to excess erosion or otherwise to improve quality/safety and reduce maintenance.








My first thought without looking anything up was that it was resin and hardener already mixed - cured epoxy.