What a stroke of luck: you're both right. To be slightly more serious, if significantly more semantic, stylistic convention has it that there are broadly three ways of applying the term 'communist' to the Soviet Union:

• Capital-c 'Communist': Used to refer to countries or people ruled by or affiliated with an official Communist Party. This is the sense in which we refer to, for example, 'the Communist bloc'.

Applicable to the USSR: Yes. The Soviet Union is obviously counted amongst these.

• Small-c 'communist': This is a more general term that refers to a host of far-left and, typically but not always, Marxist ideologies or movements. So one might be a communist who isn't a member of an official Communist Party (eg Trotsktists). This produces the question of whether Soviet policies were broadly in line with Marxist thought.

Applicable to the USSR: Depends on who you ask. Marxist-Leninists (official ideology of the USSR) would obviously insist that the Soviet Union was following Marx's philosophy and looking to create a communist society (see below). Most others on the Left take a look at the repression and hardships of Stalinism and strongly disagree. It is ultimately a question of ideology however.

• Communism as a societal stage: Marx posited that following capitalism there would be two stages of communism: the lower (in which classes exist) and the higher (which is classless). Confusingly, convention has it, following Lenin's State & Revolution, that the lower phase is called 'socialism' and the higher is called 'communism'. That is, a communist society is one in which classes no longer exist.

Applicable to the USSR: No. The Stalin Constitution of 1936 claimed, to some mirth amongst the populace, that the Soviet Union had reached the socialist stage of development. In 1961 Khrushchev promised that 'communism' would be built by 1981 but this was quietly forgotten by the state. The Soviet Union never claimed to be communist in this sense.

The debate is usually around the second point. Was the Soviet Union travelling towards a communist society, even if it hadn't reached it? But this is an ideological question that isn't really for historians to answer. There is no set template of Marxist policies that we can measure/evaluate the USSR on. We can note the grotesque hypocrisy of the Stalin years (eg Donald Filtzer and Kevin Murphy) but you'd be amazed how some apologists (eg Grover Furr) can move the goal posts to handwave away apparent anti-worker policies.

Just like the modern day ruling parties of Laos, Vietnam, Cuba and China the Soviet Union was formally not a communist society but one that was laying the groundwork for a communist society and defending the fruits of the revolution from reactionary forces abroad.

To your girlfriend you could show large Soviet posters promising that communism would be achieved in the future or cite the Communist Party of China still regularly declaring Communism as their ultimate goal.

By Lenin's The State and Revolution the state will be used first to defend the revolution against the reactionary bourgeoisie at home and abroad. And once the bourgeois have all been beaten it can wither way.