What to call a baby bird can vary depending on the species and age of the bird. The name for a baby bird varies by species, which means there's not one unifying term to describe all baby birds. Instead, the generic term for a baby bird is 'chick'.
There are three different names for baby birds, that change depending on the bird's age and life stage.
Juvenile is the term that's the equivalent term for teenagers for birds. They are at a stage of their life where they are mostly capable of fending for themselves if necessary but still partially rely on their parents for food and protection.
A Juvenile Blackbird being fed
Some species of birds have unique names for their young. Some examples of these are: