In “Effective Altruism: Introduction” (Essays in Philosophy: Vol. 18: Iss. 1, Article 1, doi:10.7710/1526-0569.1580), William MacAskill proposes a definition of effective altruism. I think having a definition is useful. It could allow effective altruists (and their critics) to have better, clearer conversations, and to avoid misconceptions.
In MacAskill's quote below, I have emphasised in bold some notable features of the definition.
As I and the Centre for Effective Altruism define it, effective altruism is the project of using evidence and reason to figure out how to benefit others as much as possible, and taking action on that basis.
On this definition, effective altruism is an intellectual and practical project rather than a normative claim, in the same way that science is an intellectual and practical project rather than a body of any particular normative and empirical claims. Its aims are welfarist, impartial, and maximising: effective altruists aim to maximise the wellbeing of all, where (on some interpretation) everyone counts for one, and no-one for more than one. But it is not a mere restatement of consequentialism: it does not claim that one is always obligated to maximise the good, impartially considered, with no room for one’s personal projects; and it does not claim that one is permitted to violate side-constraints for the greater good.
Effective altruism is an idea with a community built around it. That community champions certain values that aren’t part of the definition of effective altruism per se. These include serious commitment to benefiting others, with many members of the community pledging to donate at least 10% of their income to charity; scientific mindset, and willingness to change one’s mind in light of new evidence or argument; openness to many different cause-areas, such as extreme poverty, farm animal welfare, and risks of human extinction; integrity, with a strong commitment to honesty and transparency; and a collaborative spirit, with an unusual level of cooperation between people with different moral projects.