1. Composed of many parts: This is the most common meaning of complex. It refers to something that is made up of many different elements or components.
Example sentence: The human brain is a complex organ with billions of neurons.
2. Difficult to understand or explain: This meaning is often used for ideas or situations that are intricate and require careful consideration.
Example sentence: The relationship between the two countries is very complex, with a history of both cooperation and conflict.
3. Involving intricate processes or relationships: This meaning is often used for things that are elaborate and involve many interconnected parts.
Example sentence: The company has a complex system for managing its finances.
4. Involving both real and imaginary components (mathematics): This meaning refers specifically to complex numbers, which are used in advanced mathematics and engineering.
Example sentence: The roots of this equation are complex numbers.
It's important to pay attention to the context to understand the meaning of "complex" in a specific situation.