This is the 24th most frequent Russian word.
было
"Было" - "was" or "there was."
past tense indication of the state 'it was'.
Вчера было холодно.
Yesterday it was cold.
conditional mood 'it would have been' indicating potential situation.
Было бы лучше остаться дома.
It would have been better to stay at home.
past tense indication of existence 'there were'.