NEMA stands for National Electrical Manufacturers Association, a standardization body that defines the size and characteristics of electric motors.  A stepper motor is a type of electric motor that rotates in discrete steps.
Here's what characterizes a NEMA 17 stepper motor:
Size: It has a standard faceplate size of 1.7 x 1.7 inches (43.18 x 43.18 millimeters).
Torque: NEMA 17 comes in various torque options, but generally offers a good balance between size and power. There are high-torque versions available as well.
Applications: These motors are commonly used in
3D printers for moving the print head or bed
CNC machines for precise tool control
Robotics for controlled movement
Automation systems
Camera sliders