What is the meaning of React?

To act or perform a second time; to do over again; to reenact.

To return an impulse or impression; to resist the action of another body by an opposite force

To act upon each other; to exercise a reciprocal or a reverse effect, as two or more chemical agents; to act in opposition.

To cause chemical agents to react; to cause one chemical agent to react with another.

To post a reaction (icon or emoji indicating how one feels about a posted message).

An emoji used to express a reaction to a post on social media.

a video reviewing or responding another video (not necessarily as a real-time reaction)

Source: wiktionary.org

See also