A 3D scanner can best be thought of as a 3D Camera. The main difference is that the scanner also measures the distance to the object being scanned, this gives the 2D camera image measurement attributes.
3D scanners are generally divided into two categories, Laser scanners and Structured Light scanners.
Laser Scanners are generally for larger objects and structured light for high detail scans of smaller objects.
Large structure being scanned by a terrestrial laser scanner
45 mm sea shell scanned with a Structured Light scanner.