A replicator is a device that uses transporter technology to dematerialize quantities of matter and then rematerialize that matter in another form. It is also capable of inverting its function, thus disposing of leftovers and dishes and storing the bulk material again.
Replicators are capable of producing something as fresh and tasty as non-replicated foodstuffs, inorganically materialized out of patterns that are used by the transporters. Most people found replicated foods and drinks to taste exactly the same as non-replicated food, although some people will claimed to be able to tell the difference. Furthermore, many replicators could be programmed to produce foodstuffs of acceptable "nutritional value".
In addition to foodstuffs, replicators could be used for replicating machine parts, clothing or other objects, and although clothing can be replicated for general wear, people are prohibited to use their replicators to allow themselves to replicate official military uniforms. Industrial replicators could even be used to replicate heavier machine parts.
People with replicators are also prohibited to produce fatal poisons. Furthermore, replicators have biofilters which could screened out all contaminants, if said person who owns one wants to.
On military installations and starships, if a person in custody is confined to quarters, it is standard policy to disable the replicators that the person has access to, in order to ensure that a weapon cannot be replicated.
The first replicators developed prior Humans was the replicators used by the Greys.