Because we don't really know what cocktail means either, according to Google:

"A cocktail dress code is a semi-formal dress code that is more elegant than casual wear but less formal than black-tie. For women, this typically means a knee-length or midi dress, and for men, a suit or a dark jacket with dress pants. It allows for more flair in terms of colors, patterns, and fabrics, such as silk, lace, or satin, and is a step up from smart casual."

In reality, we don't want to set a strict dress code, we just thought we'd try and give you a little bit of direction. We personally think a wedding is a good excuse to dress up and we'd like you all to look and feel your best and be your truest self. Please dress warmly as it will be winter and try and pick appropriate footwear for walking over grass and gravel paths. We look forward to seeing all of your lovely faces!