OK–I’ve got a pretty good musical background, but I must admit, the first time I heard the word “cent” used in describing pitch was when I came over to the dark side of whistledom…what is it? What does it measure? 
http://hyperphysics.phy-astr.gsu.edu/hbase/music/cents.html
long story short, there are 100 cents in a semitone.
So, if your F is 50 cents sharp, it’s half-way to F#. I read somewhere that trained musicians can hear if someone’s out of tune by as little as a couple cents, but that untrained musicians usually can’t hear out of tune-ness less than around 10 cents. I know this was true for me when I first started learning the whistle…but as with all generalities, your mileage may vary
Cent means a hundredth fraction. It’s used in fine tuning, to measure pitches against, usually, A:440. Electronic tuners are used. One can buy them at music stores, or there are software ones you can download.
and there’s 100 cents in a dollar 
and there’s 100 cents in a dollar
Hah! That’s what I was thinking! LOL 
…and I get it now–Thanks everyone for the help! 
I guess I’ve never heard of “cents” before because I tune to an electronic keyboard. When I make flutes and whistles, I’m tuning by ear. It doesn’t seem difficult to me, but then, I’ve always tuned by ear, so maybe I’ve had enough ear training to go by!
These days you can buy decent chromatic electronic tuners for around $20 or so. If you’re making whistles, they’re well worth it. Great for tuning strings too.
Try this for a free tuner
http://www1.ocn.ne.jp/~tuner/tuner_e.html