The dress you posted is a little more formal and dare I say “prom”-y. It reminds me of something a younger woman would wear to look sexy. I.e. one who defaults to showing more skin to be sexy. I think another way to be sexy is to show/not show. Think about longer sleeves with a plunging neckline, a midi length with a good side slit, and/or like you said, low back. You can also try a one shoulder look. As for length: midi, knee length and mini over floor-length is typically semi formal. https://www.nordstrom.com/s/7753231?color=410 https://www.nordstrom.com/s/7345189?color=410 https://www.nordstrom.com/s/7570120?color=040 https://www.nordstrom.com/s/8189370?color=310&size=large https://www.nordstrom.com/s/8259536?color=400 More on reddit.com

i like all of these, so hard to decide! what color heels are you planning on wearing, and what color is your hair? More on reddit.com

A super simplified down description of the difference is that formal is generally a long dress or gown, and semi formal is short. There are exceptions - like a jersey maxi dress could be too casual for either - but a short black dress is most likely semi-formal. If you went to high school in the US, you can think of prom as formal and homecoming as semi-formal. More on reddit.com

Many couples are not familiar with dress codes at all, so sometimes they have no idea what they are actually asking for. Often they think semi formal is one step below formal , but it is not. Cocktail is closest to formal, then semi-formal. Semi formal does not require a floor length dress. 1. Semi-Formal or Dressy Casual Part of dressing for a semi-formal , or dressy casual, wedding is paying close attention to when the ceremony will take place. For evening events, darker, more formal colors are best, whereas light hues and airy fabrics are preferred for daytime affairs. Women can wear below-the-knee dresses, slip dresses, a dressy skirt and top, or an elegant pantsuit (styled with heels, nice wedges, or formal flats). 2. Semi-formal wedding attire may seem like one of the trickier wedding guest dress codes to nail. And, since cocktail and semi-formal wedding attire can sometimes be used interchangeably, you might feel confused when it's time to pick an outfit. "Semi-formal falls in the gray area between casual and formal," says Coleman. "However, cocktail attire tends to be a little more dressy than semi-formal." So, what do you wear to a semi-formal wedding? "Some ideas include a midi dress, a chic jumpsuit, or a wrap dress," Coleman continues. "For cocktail attire, stick to a structured dress or a sleek black dress—you can never go wrong with an LBD." Embellishments and additional features on an outfit can also help differentiate cocktail attire from semi-formal wedding attire. "A dress for a semi-formal wedding might not include any sort of beading or statement accessories," says Durham. I would look for a midi dress, what your MOH friend calls close to floor length. More on reddit.com