Clones
A clone is either a complete genetic copy of a living organism or a subset of its genes. In biological research and engineerinig, the term 'cloning' simply means making copies of a particular gene or genes.
Clones in Sci-fi
Like many scientific concepts, cloning has been thoroughly misunderstood by people who write science fiction. Shows like Star Trek portray the cloning process as manufacturing a complete mature adult from scratch, as seen in the accompanying picture from the TNG episode "Up The Long Ladder".
The clones are also often shown possessing skills that take years to learn for a 'normal' human(oid) as is the case with the Jem'Hadar which are grown and combat ready in a matter of days. In the film 'Multiplicity' the clones even had the complete set of memories of the original person donating his genetic material. The clone at first believed himself to be the original person. To say this is not how cloning works is an enormous understatement.
For all their other fanciful or unrealistic aspects, films like 'Star Wars' and 'Jurassic Park' show a far more accurate portrayal of cloning. Cloning a whole organism is very similar to having identical twins. The clone needs to go through the same growth and learning processes as a regular organism. In Star Wars, Attack of the Clones, we witnessed the clones in various phases of embryonic development, childhood and adults. In 'Jurassic Park', we saw the cloned dinosaurs hatching from eggs.