How humid is New York City during autumn and winter?

I'm wondering whether I should buy a humidifier - I check weather.com and it'll report that the dew point is, for example, 43 degrees F and that the corresponding humidity is 67%. 67% seems pretty high (compared to an arid, desert environment). Is 67% relative? what is this a measure of exactly? Is there a better way to find out how much moisture is in the air? Thanks