Short answers, pulled from the story.
An organism is any living thing that functions as an individual. The most common criteria for being an organism are autonomous reproduction, growth, and metabolism, though few proposed criteria are widely accepted.
Viruses are not typically considered organisms because they cannot reproduce, grow, metabolise, or maintain homeostasis on their own. They have no metabolism and rely entirely on a host's machinery to replicate, though they do have their own genes and evolve.
David Queller and Joan Strassmann proposed that cooperation should be the defining trait of an organism. They argue that organismality evolved socially, as groups of simpler units from cells upwards came to cooperate without conflicts, which would treat lichens and anglerfish partnerships as organisms.
In his 1790 Critique of Judgment, Immanuel Kant defined an organism as both an organized and a self-organizing being. The term organism first appeared in English in the 1660s, meaning an organic structure or organization.
A siphonophore is a jelly-like marine animal composed of organism-like zooids that together look and function much like a jellyfish. The philosopher Jack A. Wilson placed it in the boundary zone between being a definite colony and a definite organism.
The RNA world is a hypothetical stage in the history of life on Earth when self-replicating RNA molecules reproduced before DNA and proteins evolved. According to the hypothesis, organisms emerged when RNA chains began to self-replicate, initiating heritability, variation of type, and differential reproductive output.