I am quoting the World Socialist Movement:
When it is established it must be on a global basis, as a real alternative to the present system. In a socialist society there will be common ownership of the Earth by its inhabitants and no minority will dictate to us that production must give priority to profit. There will be no owners. The people of the world will share the world. Production will be for use, not sale. The only questions we will need to ask about production are what do people need and can these needs be met. Science and technology will at last be used to their fullest potential and in the service of humanity. The basic socialist principle will be that people give according to their abilities and take according to their needs. There will be no buying or selling, as money will have been abolished and will not be necessary in a world of free access. Socialism will mean a world without borders or frontiers, social classes or leaders, slates or governments, force or coercion.
Isn’t socialism what they had in Russia, or in China or Cuba, or in Sweden?
No. Socialism, as understood by the World Socialist Movement, was never established in any country. A short definition of what we understand to be socialism:
a system of society based upon the common ownership and democratic control of the means and instruments for producing and distributing wealth by and in the interest of society as a whole.
If there are wages and salaries, it is not socialism.
State ownership is not socialism.
Social programs are not socialism.
Socialism means democracy at all levels of society, including the workplace.
Socialism means a wageless, moneyless society.
Socialism means voluntary labour.
Socialism means free access to the goods produced by society.
With this understanding of socialism, the Socialist Party of Great Britain noted in its journal, the Socialist Standard (August 1918, page 87), that the supposedly “Marxist” Russian Revolution of November 1917 was not socialist.
A more exact explanation of what is socialism you can find by visiting The World Socialism Movement site.