Various answers, discussions, and even debates have attempted to answer this question.
Dr. R. Albert Mohler Jr., President of Southern Baptist Theological Seminary in Louisville, Ky.. gives an excellent answer and explains why the correct understanding is essential.
Indeed, the reason why the correct answer is essential is more important than the answer itself.
The video version of the answer was presented at the Ligonier Conference in June 2010.
The written answer is the text of his Keynote speech given at the banquet celebrating the 40th Anniversary of the founding of the Institute for Creation Research
To see the excellent video version (about an hour) of the answer to this question, HERE’S THE LINK
Or if you would prefer to read the answer in a written article, HERE’S THE LINK
Actually you should do both.