In Shores of Hazeron, the term citizen is mainly used for NPC characters, that are of a sentient species. Therefore, in terms of the game, a citizen can refer to any of the following:
Citizens make up the populace of a city and are the hard working inhabitants, who pass all day, to move forward production and construction. Their numbers are expressed as population and are for the most part hidden out of sight.
City morale affects whether citizens migrate into a city or away from it. This means, that a negative morale causes the citizens to become unhappy and leave, while a positive morale makes citizens spread the word about how great their city is, causing in a steady immigration of new inhabitants. The morale of the populace is affected by the social and living conditions within the city. Especially taxation, available housing and special amenities, such as hospitals, a police station, etc. have an impact on the morale.
Cities start with no population at all, when founded. When empty homes are constructed, citizens begin to immigrate to the city. Habitable worlds with plant and animal life, in addition, may have an indigenous population living in the wilderness. These people migrate into empty cities or such places, where the morale is positive. In harsh environments and on frontier worlds, a city must be connected by space for immigration to occur. The population of cities also increases due to normal reproductive growth, giving birth to children. The population of a city will however not grow to exceed the number of available homes.
Citizens work in a city, performing a variety of jobs. They generally prefer a balance where their population slightly exceeds the number of jobs. This translates into "time off" shared between the citizens. Citizens also apply some priority to the jobs they perform.
- In habitable environments, citizens work the food producing jobs first, then the power producing jobs, then the remaining jobs if there is any manpower remaining.
- In harsh environments, citizens work the power producing jobs first, then the refineries, then the food producing jobs and lastly the remaining jobs, manpower permitting.
- Refineries now stop considering their job to be essential if their storage capacity is more than 10% full of air.
- Farms stop considering their job to be essential if their storage capacity is more than 10% full.
Update 9-10-2018 - 
Citizens do not work in the absence of light except in harsh environments where their survival depends on working. In order to allow citizens to work at night on habitable planets, they require electrical energy. If no power plant and/or no energy is present, citizens will leave their work at dawn.
It is possible, to visually see if electricity is present or not: in cities without energy, the windows and streetlights are lit dim, like candlelight. Once energy is present, the windows and streetlights are lit brightly, using electrical power and lights.