A "First-Class Object" in programming refers to entities that can be treated like any other variable. This means they can be created, modified, passed as arguments, and returned from functions. Examples of first-class objects include functions in languages like JavaScript and Python, where they can be assigned to variables or passed around just like numbers or strings. In contrast, some programming languages have constructs that are not first-class objects, meaning they cannot be manipulated in the same flexible way. For instance, arrays in certain languages may have limitations on how they can be treated compared to first-class objects. This concept is fundamental in understanding how different programming languages handle data and functions.