Before I begin, I want to emphasize that not all Pagans are Wiccan, and therefore not all Pagans follow Wiccan teachings (which include the Rede). To further muddy the waters, not all Wiccans view the Rede in the same way or follow it to the same extent.
First of all, what is the Rede? The Wiccan Rede is actually a longer piece of poetry, but it is often condensed down to the last line: "An it harm none, do what you will." That is also often shrunk further to simply "Harm None". It's a simple idea, but one that can have deeply reaching consequences, depending on your interpretation.
Is it possible to have a religion that is only bound by one rule? Well, we like to think so, but many people who follow Judeo-Christian religions find it difficult to grasp.
Some people refer to the Rede as a rule, a law, or even a commandment. But others see it as more of a guideline to be applied to the best of your ability given the circumstances. The guideline viewpoint may be seen as wishy-washy to some, but it does offer more flexibility when making decisions in life. So few things are truly black and white, and you should remember that when applying the Rede.
Now the meat of it. What does "Harm None" even mean? Well, you probably already have a pretty clear idea what that means, but you shouldn't assume that your interpretation is the only one. Here are some variations on this that might make you stop and think for a moment about how you see "Harm None":
These are just a few examples of areas some people consider to be 'gray areas' when deciding where to draw the line of "Harm None". You may agree with or disagree with all the points I've mentioned, and that is just fine. How you choose to live by the Rede is your decision.
Bide you the Wiccan laws you must, in perfect love and perfect trust.
Live and let live, fairly take and fairly give.
Cast the circle thrice about, to keep the unwelcome spirits out.
To bind the spell every time, let the spell be spake in rhyme.
Soft of eye and light of touch, speak little and listen much.
Deosil go by the waxing moon, chanting out the Wiccan rune.
Widdershins go by the waning moon, chanting out the baleful tune.
When the Lady's moon is new, kiss your hand to Her times two.
When the moon rides at Her peak, then the heart's desire seek.
Heed the North wind's mightily gale, lock the door and trim the sail.
When the wind comes from the South, love will kiss you on the mouth.
When the wind blows from the West, departed spirits will have no rest.
When the wind blows from the East, expect the new and set the feast.
Nine woods in the cauldron go, burn them quick and burn them slow.
Elder be the Lady's tree, burn it not or cursed you'll be.
When the wheel begins to turn, let the Beltane fire burn.
When the wheel has turned to Yule, light the log, the Horned One rules.
Heed you flower, bush and tree, by the Lady, blessed be.
Where the rippling waters go, cast a stone, the truth to know.
When you have and hold a need, harken not to other's greed.
With a fool no seasons spend, or be counted as his friend.
Merry meet and merry part, bright the cheeks and warm the heart.
Mind the Threefold Law you should, three times bad and three times good.
When misfortune is now, wear the blue star on your brow.
True in love you must ever be, lest their love be false to thee.
These words the Wiccan Rede fulfil: An it harm none, do what you will.