Every time jQuery is called, by using $() or jQuery(), internally it is creating a new instance of jQuery. This is the source code which shows the new instance:
Internally jQuery refers to its prototype as .fn, and the style used here of internally instantiating a jQuery object allows for that prototype to be exposed without the explicit use of new by the caller.
In addition to setting up an instance (which is how the jQuery API, such as .each, children,filter, etc. is exposed), internally jQuery will also create an array-like structure to match the result of the selector (provided that something other than nothing, undefined, null, or similar was passed as the argument). In the case of a single item, this arraylike structure will hold only that item.
A simple demonstration would be to find an element with an id, and then access the jQuery object to return the underlying DOM element (this will also work when multiple elements are matched or present).