The term "split personality disorder" is not used in modern mental health terminology. The correct term for what you may be referring to is Dissociative Identity Disorder (DID). DID is a specific dissociative disorder characterized by the presence of two or more distinct personality states, each with its own unique way of thinking, feeling, and behaving. These distinct personality states are often referred to as "alters."
On the other hand, having "two different sides to their personality" can be a more general description of a person's behavior or demeanor in different situations or contexts. It is not a clinical diagnosis.
The key difference between someone with Dissociative Identity Disorder (DID) and someone who has different aspects to their personality lies in the level of disruption and fragmentation of identity. In DID, the distinct personality states (alters) can be extensive and may have amnesia for each other's experiences. These personalities can sometimes take control of the person's behavior and consciousness, leading to memory gaps and confusion.
In contrast, for individuals who do not have DID or any dissociative disorder, their different sides or aspects of personality are typically part of a coherent, integrated sense of self. It is natural for individuals to have different traits, attitudes, and behaviors that they display in various situations, but these aspects are all within the same individual's consciousness, and there is no fragmentation or loss of memory between these different sides.
While DID is a complex and rare disorder usually resulting from a history of severe trauma, having different sides to one's personality is a normal and common aspect of human behavior and doesn't indicate any specific mental health condition.
It's essential to avoid using terms like "split personality disorder" in favor of accurate and respectful language. If you or someone you know is experiencing symptoms or behaviors that are causing distress or impairment, it is advisable to seek help from a qualified mental health professional for a proper evaluation and appropriate support.