If you are in energy poverty (or fuel poverty, as it is sometimes called), you or your household cannot afford to spend enough on the energy you need to cook, heat or light your home.
In Ireland, where I live now, energy poverty has a technical definition: if your household has to spend more than 10% of its income on energy, you are living in energy poverty. This is fairly typical as far as definitions go globally. Although there is no standard definition, you are generally said to be in energy poverty once energy costs account for a certain percentage of your income.
The lack of a standard definition means that for some people, energy poverty can mean going without luxuries. For others, it can be a question of life or death.