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You might want to check out the
Einstein wasn't religious node for the background to this question, but it's not required.)
It seems to me that the term religious should be clearly distinguished from words like spiritual, thoughtful, and theistic. There are a lot of words to describe people who search for meaning and pattern in the universe--"religious" describes only a subset of those people, namely those who identify themselves as belonging to a religion, a socially identifiable group of believers.
Update: The traditional defintion of "religion" implies a life directed toward God (substitute your favorite word for "the ultimate" if necessary), not toward "personal perfection." There are plenty of atheists who are very serious about becoming moral people and improving the lives of others--can they be called religious? If so, then religion is just a synonym for "moral living--" a definition which plays into the hands of religious bigots.
I would say that "religion" consists of our relationship with the ultimate and with other humans in that context...but that definition might be flawed because I'm not sure if it can be applied to religions that don't have a personal God.