Letting a word mean two different things at the same time. In other words, using at least two more or less different concepts as definitions for the same term at the same time. Normally far more subtle than jokes such as “A feather is light. What is light cannot be dark. Therefore, a feather cannot be dark.” Equivocation can also be a matter of having different conceptualizations or connotations of the same concept, which is a step towards eventually splitting them into separate concepts. A equivocation can thus be a step towards a more nuanced understanding, but it can also be a kind of magical thinking or con artistry. A discursive sleight of hand, where different things become the same thing – or a category of people gains certain characteristics - simply by virtue of language having been used in that particular way. Note that equivocation can happen without being used by a person: It can also be a matter of two or more persons talking past each other by each of them using different definitions of the same word in the same conversation. (In Swedish: ekvivokation or dubbeldefinition)
This is an abstraction of categorism.