A 'passion' is the Orthodox word for 'vice' or 'sin'. It comes from from the Greek word pathos, meaning to 'suffer' because the passions only ever lead to suffering and ultimately death.
They include gluttony, greed, lust, anger, laziness, envy and pride.
They are all expressions of selfishness, and the opposite of love.
The Orthodox Christian aim is to flee from the passions and become more like God, to be in union with God - Theosis.