What is the meaning of Reaction?

An action or statement in response to a stimulus or other event.

A transformation in which one or more substances is converted into another by combination or decomposition.

Reactionary politics; a period in which reactionary thought or politics is resurgent or dominant.

Unpurposeful behavior.

An icon or emoji appended to a posted message by a user to express their feeling about it.

reaction

Source: wiktionary.org