fly
The Spanish word 'bragueta' is translated to English as 'fly'. This term usually refers to the opening at the front of a pair of trousers or pants, which is covered with a piece of fabric and can be closed with buttons, a zipper, or other fastening devices.
The fly of his trousers was open.
In this sentence, 'bragueta' is used to refer to the fly of a pair of trousers, which is a covering over an opening join concealing the mechanism, such as a zip, velcro, or buttons, used to close the opening.
Juan forgot to zip up his fly after going to the bathroom.
This example talks about a common situation where someone forgets to zip up the fly (or 'bragueta') of their trousers after using the toilet. In Spanish, just like in English, there are colloquial phrases for this potentially embarrassing scenario.
The fly of the trousers is very narrow.
This sentence is an observation about the physical attribute of an item of clothing, specifically the narrowness of the fly (or 'bragueta') on a pair of trousers. This could imply that it might be hard to use or uncomfortable.