未定义的索引：ajax POST和/或php脚本出错？

I'm trying to send an ajax POST to a php file, however the php file sends a notice of "undefined index", and the php file never seems to receive the value i'm trying to send it. I've been searching for the answer to why this isn't working correctly, so hopefully someone can give me some insight. I'm trying to send an ajax POST to a php file,