What is the significance of the 'P' in LAMP? Why is it PHP, Perl, or Python?
It's just so happens that the most commonly used components in that part of the stack all happened to begin with a P.  It's nothing more than a coincidence. The LAMP acronym was coined before Ruby gained its current popularity levels and there's no reason why you couldn't stick Ruby in the P slot.
I'm a Java web developer that knows a bit of Python (but haven't done any Python web development), and I am curious what exactly is meant by a LAMP stack.
I understand this to be Linux-Apache-MySQL-(PHP, Perl, or Python), but I don't understand what unites these three languages other than the letter P.
Is a LAMP stack fundamentally different if Ruby was used? Using Ruby would typically mean using Rails, but Python web apps usually use Django or Pylons. Or does LAMP signify that no framework is used? Is Java web development essentially different because of Tomcat in place of Apache?