[PHP-WIN] php defining variable defaults?

[FARRINGTON, RYAN]

ok cold fusion has the ability to do a <cfparam name='' default=''> 

this lets you specify a variable name to be defaulted to a value if it is
called without being defined. I usually use this for variables specified by
forms either by GET or POST.  now I can't find it's equivalent in PHP.. can
anyone direct me in the correct direction?