jQuery OR Selector?

Use a comma.

'.classA, .classB'

You may choose to omit the space.

Using a comma may not be sufficient if you have multiple jQuery objects that need to be joined.

The .add() method adds the selected elements to the result set:

// classA OR classB
jQuery('.classA').add('.classB');

It's more verbose than '.classA, .classB', but lets you build more complex selectors like the following:

// (classA which has <p> descendant) OR (<div> ancestors of classB)
jQuery('.classA').has('p').add(jQuery('.classB').parents('div'));

I have written an incredibly simple (5 lines of code) plugin for exactly this functionality:

http://byrichardpowell.github.com/jquery-or/

It allows you to effectively say "get this element, or if that element doesnt exist, use this element". For example:

$( '#doesntExist' ).or( '#exists' );

Whilst the accepted answer provides similar functionality to this, if both selectors (before & after the comma) exist, both selectors will be returned.

I hope it proves helpful to anyone who might land on this page via google.