Most dress descriptions assume you already know the vocabulary. This is the vocabulary.
Shopping for a dress means reading words like sheath, A-line, empire and midi, usually in the same sentence and usually without explanation. They are not interchangeable, and knowing which is which saves a great deal of time.
There are two separate things being described. The silhouette is the shape of the dress. The length is where the hem falls. A dress has one of each, and almost every combination exists.
The Silhouettes
A-Line
Fitted through the shoulders and bust, then widening gradually and in a straight line toward the hem, forming the shape of a capital A. The width comes from the cut of the cloth rather than from gathering, so it hangs cleanly rather than bunching at the waist. It is the most broadly wearable shape there is.
Sheath
Fitted through the whole body from shoulder to hem, following the natural line without flaring. It is usually darted at the bust and waist to create that shape. Formal, precise, and the shape most associated with office and cocktail dressing.
Shift
Falls straight down from the shoulders with no waist definition at all. Often confused with the sheath, but a shift skims rather than follows, and it has no darting at the waist. Easy to wear and easy to move in.
Fit and Flare
Nips in sharply at the natural waist, then flares out. It is the more dramatic cousin of the A-line, with a clear break where the A-line has a gradual one.
Wrap
One panel crosses over another and fastens at the side, creating a V neckline and a diagonal seam. A true wrap ties; a faux wrap is sewn in place and pulls on. Adjustable by design.
Empire
The seam sits directly under the bust, and the skirt falls from there. It creates a long line below the bust and is the shape most often used where ease through the middle is wanted.
Shirt Dress
Built like a shirt: a collar, a button placket, often a cuffed sleeve. Usually belted or tie-waisted, which lets it read as either A-line or shift depending on how you fasten it.
Bodycon
Cut close to the body throughout in a fabric with stretch. Distinct from a sheath, which achieves its shape through tailoring rather than through the cloth.
A dress has a silhouette and a length. Learn the eight silhouettes and the four lengths, and every product description becomes readable.
The Lengths
Mini
Hem above the knee. Anything from mid thigh upward.
Knee Length
Hem at or within an inch or two of the knee. The most conservative of the lengths and the least discussed.
Midi
Hem somewhere between the lower calf and the ankle. The most useful length in a wardrobe because it is appropriate almost everywhere and accepts almost any shoe.
Maxi
Hem at or near the floor. Formal by default, though a cotton maxi in a print reads as daywear without difficulty.
Putting the Two Together
Once the vocabulary is in place, a product description becomes straightforward. An "A-line midi dress" is fitted at the top, widening gradually, ending at the calf. A "sheath midi" is fitted throughout and ends at the calf, which is a completely different garment despite sharing a length.
The pairings that come up most often are worth committing to memory. A-line and midi is the default occasion dress. Sheath and knee is the default formal dress. Shift and mini is the default easy summer dress. Wrap and midi is the one that does the most jobs.
Three Details That Change a Silhouette
The waist seam. Where the horizontal line falls changes the shape more than anything else. Natural waist, empire under the bust, dropped onto the hip, or absent entirely.
Pleating and gathering. Both add volume below the waist, but pleats fall in organized folds and gathering bunches. A pleated A-line and a gathered A-line hang quite differently.
The neckline. It does not change the silhouette but it changes how the whole dress reads. A square neck formalises, a V neck lengthens, a crew neck simplifies.
Four More Shapes Worth Recognizing
The Empire Line
The waist seam sits directly under the bust, and the skirt falls from there to the hem. It is the oldest of the shapes still in regular use and it reads as soft and slightly romantic. The thing to watch is the seam placement, since an empire line sitting an inch too low loses the whole effect.
The Wrap
Two panels crossing over at the front with a tie at the waist. The neckline is a V by construction rather than by design, and the skirt falls from the tie. It is the most adjustable shape here and the one that fits the widest range of bodies from a single pattern.
The Slip
Cut on the bias with thin straps and no waist seam, falling in a continuous line from shoulder to hem. It is the simplest construction of any dress and by some distance the most demanding fabric choice, because there is nothing else to look at.
The Tiered Dress
Horizontal panels of gathered fabric joined at seams down the skirt. Soft and full and forgiving. The detail worth checking is where the tier seams fall, since a gathered seam sitting at the widest part of the hip does the same job as a badly placed hem.
Telling Them Apart in Ten Seconds
There is a quick method that works on almost any dress, on a rack or in a photograph.
First, find the waist seam. Is there one? If not, it is a shift, a slip or a column. If there is one, where does it sit? Under the bust is empire. At the natural waist is A-line, fit and flare or sheath. At the hip is a drop waist.
Second, look at what the skirt does below that seam. Falls straight down means sheath or column. Widens in a straight line means A-line. Flares sharply means fit and flare. Gathers into panels means tiered.
Third, look at the closure. A crossover with a tie is a wrap. A button placket down the front is a shirt dress. Neither of those is really a silhouette, but both are how dresses get named in shops.
Those three questions will identify almost any dress you are looking at, and more usefully they tell you how it will behave when you put it on.
Why This Is Worth Knowing
Not for the vocabulary. The reason to know the shapes is that it turns online shopping from guesswork into something closer to a decision. A product description that says fit and flare tells you the skirt will not touch your hip and that you will be able to sit comfortably through a dinner. One that says sheath tells you the opposite. Neither photograph will tell you that, and the word does.
The Shapes in the Collection
Common Questions
What Kind of Dress Is This?
Identify it by two things: the silhouette and the length. Look at where the waist seam sits and whether the dress follows the body or falls away from it, then check where the hem lands. Those two answers name almost any dress.
Eight silhouettes and four lengths cover almost everything on almost any rack. Once you can name the shape you are looking at, you can tell from a product description alone whether a dress will do what you want, which saves a great deal of ordering and returning.