A written agreement by the program participants to voluntarily participate in an evaluation or study after having been advised of the purpose of the study, the type of the information being collected, and how information will be used.
www.ojp.usdoj.gov/BJA/evaluation/glossary/glossary_i.htm

The process in which a person learns key facts about a clinical trial or research study and then agrees voluntarily to take part or decides against it. This process includes signing a form that describes the benefits and risks that may occur if the person decides to take part.
www.cancercare.mb.ca/CIO/cio_glossary.shtml

The voluntary verification of a patient's willingness to participate in a clinical trial, along with the documentation thereof. This verification is requested only after complete, objective information has been given about the trial, including an explanation of the study's objectives, potential benefits, risks and inconveniences, alternative therapies available, and of the subject's rights and responsibilities in accordance with the current revision of the Declaration of Helsinki.
www.wcctrials.com/glossary.HTM

For information on the Declaration of Helsinki
www.cirp.org/library/ethics/helsinki/

An individual willingly agrees to participate in an activity after first being advised of the risks and benefits.
Source: Human Genome Project Information

The permission granted by a participant in a research study (including medical research) after he/she has received comprehensive information about the study. This is a statement of trust between the institution performing the research procedure and the person (eg, a patient) on whom the research procedures are to be performed. This includes the type of protection available to people considering entering a drug trial. ...
www.amfar.org/cgi-bin/iowa/bridge.html

The ongoing dialogue between researchers and participants that addresses patient concerns and questions and ensures patient protection throughout the trial
www.gene.com/gene/pipeline/trial-education/glossary.jsp

Before patients make the decision to participate in a clinical trial, they are given detailed information about the study, including what treatments will be tested, the possible side effects and the time commitment required.
www.seattlecca.org/patientsandfamilies/WhatAreClinicalTrials/Definitions.htm

The process of learning key facts about a clinical trial before participating, including:
www.mdsupport.org/glossary.html

Consent by a patient to a surgical or medical procedure or participation in a clinical study after achieving an understanding of the relevant medical facts and the risks involved. The American Heritage® Stedman's Medical Dictionary, 2nd Edition Copyright © 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

Informed Consent defined by the AMA:
From: http://www.ama-assn.org/ama/pub/category/4608.html

Informed consent is more than simply getting a patient to sign a written consent form. It is a process of communication between a patient and physician that results in the patient's authorization or agreement to undergo a specific medical intervention.

In the communications process, you, as the physician providing or performing the treatment and/or procedure (not a delegated representative), should disclose and discuss with your patient:

The patient's diagnosis, if known;
The nature and purpose of a proposed treatment or procedure;
The risks and benefits of a proposed treatment or procedure;
Alternatives (regardless of their cost or the extent to which the treatment options are covered by health insurance);
The risks and benefits of the alternative treatment or procedure; and the risks and benefits of not receiving or undergoing a treatment or procedure.

In turn, your patient should have an opportunity to ask questions to elicit a better understanding of the treatment or procedure, so that he or she can make an informed decision to proceed or to refuse a particular course of medical intervention.

This communications process, or a variation thereof, is both an ethical obligation and a legal requirement spelled out in statutes and case law in all 50 states. (For more information about ethical obligations, see the AMA's Code of Medical Ethics, contained in the AMA PolicyFinder. Providing the patient relevant information has long been a physician's ethical obligation, but
the legal concept of informed consent itself is recent.