No-one can agree on a definition
Euthanasia - a good death
That's what it literally means. You can't use that definition in ethics, as it makes a value judgement about the issue. Any of the following may be found:
Physician-assisted suicide - a doctor provides drugs that will end a patient's life. Usually the patient would take the drugs themselves. If the doctor administers the drugs, it is:
Active euthanasia - medication is given with the express purpose of shortening someone's life
Passive euthanasia - the withdrawal of life-sustaining treatment, leading to someone's death.
Legally, many of these words need more careful definition. For example, does feeding a patient count as a treatment (it has done since 1989 in the UK)? In the Uk in 2006, euthanasia is illegal, but doctors can withdraw treatment even without specific consent (see the Tony Bland case).
Euthanasia can be voluntary (where the patient makes a specific choice), non-voluntary (where the patient is not in a position to make a choice, e.g. in a Persistent Vegetative State) or in-voluntary (where the patient does not want to die).
A useful working definition might be:
The deliberate killing of a person for their own benefit
