"Also known as Falcon 9 Heavy, it is a reusable heavy space lift vehicle
designed and manufactured by SpaceX. A variant of Falcon 9, the concepts
were discussed in mid-2000. The plan was made known to the public in April
2011 and broadcasted it's expected test flight in 2013. The challenges of
making Falcon Heavy was more difficult than they thought and postpone
the initial test flight to December 2017. The ardous task was to combine 3
Falcon 9 cores together. Each first stage consists of a cluster of 9
Merlin engines and the total of 27 rocket engines.
The Falcon Heavy will consists if strenghtened Falcon 9 rocket core and two Falcon 9 first stages as strap-on boosters. It can lift 54 metric tons or a mass equivalent of a Boeing 737 fully loaded. It can generate a trust about 18 Boeing 747 planes.
It is designed to carry humans into space and crewed missions to Moon and Mars. Falcon Heavy is able to deliver large payloads to orbit and also carry its own Dragon spacecraft.
(Source: spacex.com & en.wikipedia.org/wiki/Falcon_Heavy)