Effective altruism: Effective altruism (EA) is the name of a growing social movement and an idea – based around using evidence and reason to find the most effective possible ways of doing good in the world. An effective altruist is someone who identifies with and tries to act according to the principles of Effective Altruism.
Cost-effectiveness: The cost-effectiveness of a charitable intervention simply refers to how much good it does with a certain amount of resources. The cost-effectiveness of a donation to a charity typically refers to how much good the donation does on the margin e.g. if you donate $100 to a charity, how much extra impact will be produced.
Impartiality: Impartiality is the valuing of all lives equally, independent of location, age, gender, etc.
Cause-neutrality: One is cause-neutral if one chooses where and how to help (e.g. which charity to donate to), only based on how much doing so would help. That is to say, one does not have a “pet cause.”
Prioritization: Cause areas can be evaluated in terms of their scale (how large is the problem and how much would it help to solve it), tractability (how easy is it to make progress) and neglectedness (how many resources are already dedicated to this problem) .
Counterfactual reasoning: Counterfactual reasoning looks at how much impact an action has relative to what would have happened otherwise. Your counterfactual impact would then be the amount of extra good done through your action.
Leveraging donations: Sometimes, charitable donations can be leveraged to increase their effect. For example, instead of donating $1000 to charity, one might use the $1000 to hold a fundraiser event which results in the donation of more than $1000.
Consequentialism: Consequentialism is the view that the rightness of an action depends only on its consequences, that is whether the states of the world it causes are good or bad. Most effective altruists are consequentialists.
Utilitarianism: Utilitarianism is a particular consequentialist moral theory, which states that an act is good or bad according to the extent to which it increases happiness and decreases suffering.
Population ethics: Population ethics asks questions such as whether it is better to bring about a larger total amount of happiness in the world (e.g. by having a higher population that is less happy) or a smaller population who are happier on average, and whether we ought to count causing new happy people to be born in the future as equally important as making people who currently exist happy. Population ethics is a source of significant disagreement among philosophers in general as well as effective altruists.
Rationalism: Rationalism is an approach to improving one’s thinking and an associated community, interested in studying cognitive biases, statistics.
Earning to give: Earning to give refers to the practice of choosing a career not for its direct impact but for its salary, and then donating a significant portion of this salary to effective charities. Earning to give can sometimes be more effective than direct work, through your donations allowing others to do more good than you would directly.
Pledge (GWWC & TLYCS): Many effective altruists sign pledges to donate a significant portion of their incomes to charity. Members of Giving What We Can pledge at least 10% of their income to the charities they believe to be the most effective. TLYCS has a similar pledge. A more general pledge is available at http://effectivealtruismhub.com/donations.
X-Risk: An existential risk is a danger that is global in scope and terminal in intensity. That is, it threatens to “either annihilate Earth-originating intelligent life or permanently and drastically curtail its potential.” Examples include severe climate change, nuclear warfare, and unfriendly artificial intelligence.
Meta-EA: A meta-EA charity is an organization which contributes indirectly by seeking to build the effective altruism movement or increase its efficiency. Examples include GiveWell, CEA, TLYCS, and MIRI.