sometimes called the systerm board is the main circuit board of the system unit

That’s absolutely correct! The main circuit board of the system unit is indeed sometimes called the system board, but the more common terms are:

• Motherboard (This is the most widely used term)
• Mainboard

These terms all refer to the same crucial component that houses the central processing unit (CPU), memory (RAM), and other essential components that enable communication and functionality within the computer.