"Night owl" people are people that stay up real late at night, maybe even all night. I used to be one.
I'm a night owl as well. I sleep better during the day. I have always been an insomniac.
I'm still not an 'early bird' though, which is someone who starts sleeping at an early time and wakes early.
I'm not either. If I have to wake up early, I'm a bit cranky.
In Scandinavia, early birds are referred to as "A-people" and night owls are called "B-people" hehe, so I guess that makes me a C-person.
Wonder what they would call someone who goes to sleep late and can't stay asleep? lol
Researchers traditionally use the terms "morningness" and "eveningness" for the two chronotypes or diurnality and nocturnality in animal behavior. In several countries, especially in Scandinavia, early birds are called "A-people" and night owls are called "B-people".
Etymology.
The term is derived from the primarily nocturnal habits of the owl. Most owls sleep during the day and hunt for food at night.
Characteristics.
Usually, people who are night owls stay awake past midnight, and extreme
Night owl (person)
A night owl, evening person or simply owl, is a person who tends to stay up until late at night, or the early hours of the morning. Night owls who are involuntarily unable to fall asleep for several hours after a normal time may have delayed sleep phase syndrome. 
The opposite of a night owl is an early bird – a lark as opposed to an owl – which is someone who tends to begin sleeping at a time that is considered early and also wakes early.