Cursor is a:

This question defines the term 'cursor' in the context of computer interfaces. It's important to distinguish between the visual indicator and the devices or components associated with it.

The correct answer is Thin blinking line. Specifically, an 'insertion point cursor' or 'text cursor' is represented as a thin, often blinking, vertical line or a block that indicates where the next character typed will appear on the screen. This is its primary visual form when interacting with text input fields.

• Pointing device is incorrect because a pointing device (like a mouse or trackpad) is the hardware used to control the cursor's position on the screen, but it is not the cursor itself. The cursor is the on-screen visual representation.
• Pixel is incorrect. A pixel is the smallest individual unit of a digital image or display. While a cursor is composed of many pixels, it is not a single pixel; it's a collection of pixels forming a specific shape or line.
• All of these is incorrect because options B and C are not accurate definitions of a cursor.

Therefore, the most precise description of a cursor, especially in text-based interactions, is a thin blinking line.