Here is the problem. The far left has a long tradition of using words to achieve political ends without regard for consistent use or clear meaning. They seem to really like fuzzy concepts and flexible vocabulary.
What is "communism" - a political system? An economic system? A set of policies imposed by a communist party? A sociopolitical movement? A specific stage of historical development?
How can one know what a communist is without knowing what communism is?
Here is a some material from Wikipedia: "Communists such as council communists and non-Marxist libertarian communists and anarcho-communists, as well as some Marxist-Leninists who have progressively abandoned many of the basic assumptions of Leninism, oppose the idea of a vanguard party and a transition stage, and advocate for the construction of full communism to begin immediately upon the abolition of capitalism."
So, there are lots of different kinds of communists recognized by those in the academic far left: Council communists, non-Marxist libertarian communists, Stalinists, Trotskites, anarcho-communists, Marxist-Leninists, Maoists, Christian communists, etc.
They all share this: They have a central control to ensure distribution: every person should contribute to society to the best of his or her ability and consume from society in proportion to his or her needs. They have no private property, then no one keeps any of what they produce except what they need to consume with the rest being distributed to those who don't produce all that they need. They advocate some form of control to prohibit the private property and to enact the distribution (Note: I have no idea what the various anarchist-communists posit as control, or alternatively, how they explain distribution without it - and I dont care.)
Historically, the concept of ability producing, some control that governs distributing, and the idea of need determining consuming, and no private property is a concept that goes back earlier than Marx - at least the general idea, if not the details of the control mechanism.
French communist Morelly, proposed in his 1755 Code of Nature "Sacred and Fundamental Laws that would tear out the roots of vice and of all the evils of a society" including:
I. Nothing in society will belong to anyone, either as a personal possession or as capital goods, except the things for which the person has immediate use, for either his needs, his pleasures, or his daily work.
II. Every citizen will be a public man, sustained by, supported by, and occupied at the public expense.
III. Every citizen will make his particular contribution to the activities of the community according to his capacity, his talent and his age; it is on this basis that his duties will be determined, in conformity with the distributive laws (Code of Nature)
Utopian socialist Henri de Saint-Simon (17 October 1760 – 19 May 1825) came later and had all of those elements.
Then came Louis Blanc in 1840, in "The organization of work", and he too provided those key elements.
And then Karl Marx, who popularied the saying, "From each according to his abilities, to each according to their need". (Wikipedia)
Politics is always an implementation of moral principles. All of the communists were drawing on altruism - take a look at the New Testement:
Matthew 25:15 And to one he gave five talents, to another two, and to another one; to each according to his ability. And he went abroad at once.
Acts 2:45 And they sold their possessions and goods and distributed them to all, according as anyone had need.
Acts 4:32-35 And the multitude of them that believed were of one heart and of one soul: neither said any of them that ought of the things which he possessed was his own; but they had all things common. And with great power gave the apostles witness of the resurrection of the Lord Jesus: and great grace was upon them all. Neither was there any among them that lacked: for as many as were possessors of lands or houses sold them, and brought the prices of the things that were sold, and laid them down at the apostles' feet: and distribution was made unto every man according as he had need.
So here we have another "From those according to their ability and to those according to their need" but it is advocated as a moral principle and does not proscribe a political control mechanism to implement the prevention of private property and to provide the distribution.
I'd say that communism is a political implementation of the altruistic/statist principle of taking from those who have the ability to produce more than they need and to distribute it to those whose needs cannot be met by what they produce. It is a system that is based upon prevention of anyone holding private property.
Since implementation is rarely 100% the question still arises as to when the principle is sufficiently in effect to stay that it is a communist state. Is it better to look at the percent of implementation? Or, to look at degree to which the principle supplants the opposing principles? Lots of confusions and imprecision in trying to make measurements.