From Diversity Style Guide:
Someone who supports a group other than their own (in terms of racial identity, gender, faith identity, sexual orientation, etc.) Allies acknowledge disadvantage and oppression of other groups; take risks and action on the behalf of others; and invest in strengthening their own knowledge and awareness of oppression.
From The Legacy Project:
Someone who challenges themselves and others about the oppressions, discriminations, and barriers that other peoples face, although they may not personally face a particular barrier or form of discrimination or oppression themselves. Examples of allies are straight allies (heterosexual people who stand up against homophobia to support lesbian, gay, bisexual, transgendered, and queer people and their rights) and Indigenous allies (nonIndigenous people who stand up against racism, colonialism, and colonial oppression to support Indigenous people and their rights). To be an ally requires an analysis of oppression: an understanding of power dynamics, looking at who holds power and privilege, and who is kept from it through various forms of oppression. Employing this analysis involves challenging systems of dominance and looking for solutions to make society more equitable.
To watch: “What does ally means to you?” by Under Our Skin Project