Just like a hose you might use to water your garden, the purpose of a hydraulic hose is to allow fluid to flow from one component to another – in this case hydraulic fluid. The hose is the conduit that ensures the fluid is able to travel unimpeded and it's a vital part of keeping hydraulics systems moving. In fact, if a hydraulic hose was to fail it can bring entire production lines to a standstill and take vital machinery offline until the hose can be replaced.
http://www.ugw-hose.com/hydraulic-hose/