Basic terms in Ruby....

• Class: A class is a definition of a concept in an object-oriented language such as
Ruby. We created classes called Pet, Dog, Cat, Snake, and Person. Classes can inherit
features from other classes, but still have unique features of their own.

• Object: An object is a single instance of a class (or, as can be the case, an instance of
a class itself). An object of class Person is a single person. An object of class Dog is a
single dog. Think of objects as real-life objects. A class is the classification, whereas
an object is the actual object or “thing” itself.

• Object orientation: Object orientation is the approach of using classes and objects
to model real-world concepts in a programming language, such as Ruby.

• Variable: In Ruby, a variable is a placeholder for a single object, which may be a
number, string, list, or an instance of a class that you have defined, such as, in this
chapter, a Pet.

• Method: A method represents a set of code (containing multiple commands and
statements) within a class and/or an object. For example, our Dog class objects had
a bark method that printed “Woof!” to the screen. Methods can also be directly
linked to classes, as with fred = Person.new, where new is a method that creates a
new object based upon the Person class. Methods can also accept data—known as
arguments or parameters—included in parentheses after the method name, as
with puts("Test").

• Arguments/parameters: The data passed to methods in parentheses (or, as in some
cases, following the method name without parentheses, as in puts "Test").

• Kernel: Some methods don’t require a class name to be usable, such as puts. These
are usually built-in, common methods that don’t have an obvious connection to
any classes. Many of these methods are included in Ruby’s Kernel module, a module
that provides functions that work from anywhere within Ruby code without
being explicitly referred to.