A class is the blueprint for an object.
An instance is an object of a class.
Basically what that code is saying is: "Only one instance of Chassis will exist, and it is this one. In order to use it you need to get it from me."
another example: the drive object in that code is an instance of RobotDrive.
Code:
private RobotDrive drive;
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Programmer - A creature known for converting Caffeine into Code.
Studying Computer Science @ Louisiana Tech University
Associate Consultant @ Fenway Group
2012-13: 3946 - Head of Programming, Electrical and Web
2014 - 3468 - Programming Mentor
2015 - Present - Lurker