/clone command

clone <x1> <y1> <z1> <x2> <y2> <z2> <x> <y> <z> [mode]

Example:
► Copy all blocks within a cubic area to another location.

/clone -260 68 260 -256 72 256 -260 68 248 replace
/clone -260 68 260 -256 72 256 -260 68 248 masked

More information:
The x y z coordinate is the lowest north-west position at the comparison location (movement from x and z is positive). Mode options are 'replace' (default) which copies all blocks, or 'masked' which copies all non-air blocks (eg. the destination can have blocks where the source may have air blocks).