I get this question a lot & I hear folks using these terms interchangeably, but really they are quite different.
The main difference: fiber.
Smoothies keep the plant fiber, juicing discards it.
Smoothies are made in a blender, juicing in a juicer.
When you make a smoothie, you generally peel, deseed, and pit whatever variety of fruits and veggies you choose, then add some water & throw into a blender. You blend until everything is smooth and drink it up.
Since smoothies keep all the plant fiber, they are more filling and can count as the better half of a meal. Plus the fiber helps you feel full longer and is important for digestion. Having a daily green smoothie keeps me feeling good & energized.
Check out How To Make The Perfect Green Smoothie.
To juice, you feed the fruits and veggies through a juicer (sometimes with skins & seeds, no water) and what comes out is a pulpless juice.
Although the yield is much smaller, you can pack in more fruits and veggies, therefore more vitamins. Some also claim juicing gives your digestion a "break".
I personally do smoothies most of the time because I want to keep the healthy fiber.
However, I have been known to make juice - like my Sunshine Turmeric Juice or Beet Carrot Clementine Juice when I want something light and refreshing. I don't own a juicer so I use my Vitamix* (WTF is a Vitamix?). To do this I generally add a small amount of water, stay away from emulsifying fruits (like banana or avocado) and strain everything after it's blended.
Whether you choose to juice or smoothie, it really comes down to preference and what you already have in your diet. If you're already consuming raw fruits & veggies daily, then juice might be a great addition. If you're on the go and want to get your greens in quick and easy, a smoothie might be best for you. Or drink a combo! Mixing it up is always good.
Got any other questions? I'd be happy to answer or discuss in the COMMENTS below...
*I just recently became a proud affiliate of Vitamix (yay!) I decided after having consulted 20 or so friends and family into getting one that it's about time I get paid for it. When you use my promo code (06-009896) at www.vitamix.com, you get free shipping (usually $25-$35) and yep, I get a commission.