Gender essentialism is the belief that a person, thing, or particular trait is inherently and permanently male and masculine or female and feminine. In other words, it considers biological sex the primary factor in determining gender.

As its deployment in such works confirms, essentialism is thought to be a bad thing. ... Yet it is also commonly argued that we cannot avoid at least some kind of essentialism: that it is a politically necessary shorthand; or even, in some arguments, a psychologically inevitable feature of the way human beings think.

An anti-essentialist definition doesn't presume that there is an essence to anything, any intrinsic qualities that we can all agree on. Instead, it defines things in terms of a loose set of attributes that we generally agree pertain to the thing we are trying to define, but we aren't too fussed about any one attribute.

1 : an educational theory that ideas and skills basic to a culture should be taught to all alike by time-tested methods — compare progressivism. 2 : a philosophical theory ascribing ultimate reality to essence embodied in a thing perceptible to the senses — compare nominalism.