Perhaps you work at an office with a stated dress code, or you've received an invitation to an event with the request to dress "business casual."

But what exactly is a business casual dress code? It turns out the answer to that question is confusing for many. 

"This one is the murkiest for our customers and for other people we speak to. Part of the problem is that there are so many trends that are so casual," Dorie Smith, cofounder of women's workwear brand Of Mercer, recently said to Business Insider.

Last June, for example, JPMorgan sent out a company-wide memo encouraging employees to dress in business casual unless they were meeting with clients. Other firms like PricewaterhouseCoopers and BlackRock (which has had a business casual dress code since the '90s) followed suit in relaxing their office dress requirements as they sought to attract millennials, many of whom like to dress in athleisure in their spare time.

But the rise of athleisure and increasingly casual workplaces has led some people to don leggings and other inappropriately casual clothing items for the office. Since more and more people are wearing leggings and other performance-centric materials as they socialize and do errands on the weekends, it seems only natural that the look would bleed into the workplace. 

Leaning into that, according to the ladies behind Of Mercer, could be a big mistake. 

 "We've even gotten emails from HR at some of these firms that say, 'Help our analysts realize it's not OK to wear leggings to work,'" Smith said. "People go too casual."

You can, however, incorporate some elements of athleisure into your work wardrobe, like tailored pants that have some stretch to them -- just no sweatpants, yoga pants, or tank tops. 

"Our rule of thumb is to make sure you're dressing one step above everyone around you," Emelyn Northway, Smith's cofounder, said. "If people are wearing jeans, wear nice black pants instead. It goes a long way to making you feel good about yourself and to making other people feel like you know what you're doing."

Recent studies have shown that wearing nice clothes in the office can actually be an effective strategy -- dressing professionally can affect the way people perceive you, how confident you're feeling, and even how you're able to think abstractly.

The Of Mercer founders recommend going for a dress with a fit-and-flare silhouette or a wrap dress in a bold color. After all, you'll never hear a manager complain that someone dresses too nicely -- but you might hear about someone who's dressed down too much.