A lightweight stroller goes from a cheap basic, easy fold stroller which can be a umbrella fold or book fold to a more elaborate stroller which can convert to a travel system or even have a reversible seat unit.
Traditional umbrella fold strollers (like a Maclaren) are often seen on every highstreet as they are light, easy to push and fold very small.
Why do you need one? We have to be honest and say regardless of which system you buy almost everyone ends up with a lightweight stroller as well. The convenience of the small fold and easy to lift means you will use this type of buggy day to day and use your full system when going out on trips etc.
At Groovystyle we like the more unusual strollers like the Micralite Superlite, the Quinny Zap and the Phil and Ted's Smart which is now has a reversible seat with the Verso option. The Quicksmart folds to almost nothing and comes with its own travel bag which will fit into an overhead locker ot an aeroplane (check with your airline in regard to baggage size/weights etc).