This document discusses series and parallel electric circuits. A series circuit has components connected one after the other so there is only one path for current to flow. If one component fails in a series circuit, the entire circuit fails. A parallel circuit has multiple paths for current and if one component fails, current can still flow through other paths. The key differences are that series circuits have the same current but total resistance is the sum of all resistances, while parallel circuits have the same voltage across all branches but current divides across the paths.