In Glossary§

See primary documentation in context for Instance

An instance of a class is also called an object in some other programming languages. It has storage for attributes and is often the return value of a call to a method called new, or a literal.

Instances of most types are defined to be True e.g., defined($instance) is True.

my Str $str = "hello";  ## this is with built-in types, e.g. Str 
if defined($str) {
    say "Oh, yeah. I'm defined.";
}
else {
    say "No. Something off? ";
}
 
## if you wanted objects... 
class A {
    # nothing here for now. 
}
 
my $an_instance = A.new;
say $an_instance.defined.raku;# defined($an_instance) works too.

To put things another way, a class contains the blueprints of methods and attributes, and an instance carries it into the real world.