Well the term comrade means friend, mate or ally. Its use suggests equality. The term is closely related to the Communist Revolution in Russia where the leaders refer to each other as comrades in their struggle to remake Russia into a communist state, like the one first envisioned by Karl Marx. This novel is an allegory of the Russian Revolution, so it is fitting that Orwell has the animals refer to each other as comrades. (but of course during the end, the comradship ends as the pigs become ruthless)
