There are many different ways to describe Rolfing®.  We've provided a number of ways below.  Feel free to borrow any of these when trying to describe to friends that you are not throwing up, rolling on the floor laughing, or doing some therapy involving the piano playing dog from The Muppets.

The technical way:

Rolfing is a system of soft tissue manipulation and movement education that organizes the whole body in gravity. Rolfing affects the body's posture and structure by manipulating the myofascial system (connective tissue). Research has demonstrated that Rolfing creates more efficient muscle use, allows the body to conserve energy, and creates more economical and refined patterns of movement.
Video of Dr. Robert Schleip describing Rolfing to a group of researchers at the Fascia Research Congress

The Fuzz Speech:

Gil Hedley's excellent youtube video on how fascia creates "fuzz" in the body that Rolfing can help to clear up.

Non-Newtonian Fluid Dynamics:

Fascia(connective tissues) behaves much like a non-netownian fluid, which is to say that when force is rapidly applied, it tends to react like a solid, but otherwise like a liquid.  If you watch the following video you can see people running on "water".  Sinking into the tissue requires a slow pressure similar to what Rolfing delivers or similar to slow static stretching.
Time Warp Video of Water and Cornstarch on Youtube

The ship analogy:

Think of the connective tissue (fascia) in your body as the rigging lines on a sailing ship.  If the rigging gets too tight or too loose in various areas, the ship may begin to list, the mast to turn the wrong direction, and the sails to sag and lose the wind.  Rolfing works to keep the rigging balanced so that the ship can sail as it was meant to.

The auto analogy:

Think of your body like a car.  In terms of bodywork, if you think of massage like an oil change (regular maintenance, keeps things running smoothly), then Rolfing is like rebuilding the transmission (fixes up systems that have gotten worn down, gives you another 100,000 miles potential, not something you want to do every 3k miles)

The reset button:

Rolfing is sometimes described as a process of "unwinding time".  Rolling back the clock on your body to a time when it functioned more naturally, operated as normal without you having to think about it.

The form/function cycle:

There is a cyclical relationship where the things we do with our body influence the shape it takes and the shape our body takes influences the way we use it.  Movement therapies like yoga, Alexander technique, dance, etc. seek to intervene in the function of the body to influence the shape.  Rolfing seeks to directly influence the shape in order to change function.  Both are useful and can influence and enhance each other's benefits in creating a healthier being.

Chiropractic for the soft tissue:

Think of the way chiropractors re-align bones.  Rolfers take similar measures to realign the connective tissue which holds together the bones and muscles but with slow deep pressure.  When used in conjunction, the effects can be especially powerful for changing the body.

Pulling taffy:

Imagine someone pulling taffy.  It stretches slowly and then past a certain point it begins to sag under its own weight and relax downward.  Rolfing works similarly on your tissues to help release tension from the muscle and allow your body to align and hang off of the bones rather than hold itself tight.

 Frank Herbert's Dune - The slow blade penetrates the shield:

If you happen to be a fan of the 1984 movie adaptation of Frank Herbert's Dune, you may recall the shield fighting scene.  In it energy shields are used to deflect fast and glancing blows, but they can be penetrated by a slow and deliberate strike.  In a similar way, Rolfing moves slowly to sink through tissues where faster motions would cause it to tense and "shield" the body from pressure.
Youtube clip of the shield practice scene