What does N+1 redundancy mean for a Modular UPS?

When the term N+1 or N+2 or N+3 is used in relation to UPS design, this refers to adding extra capacity to a system, so that if a module fails (or is removed from service) the remaining modules continue to power the load. N is the running capacity of the system and the number represents how many additional modules are available for resilience and redundancy in the UPS system design. If a module fals, the others take over automatically with no break in the critical power path to the connected load.