Meaning: This idiom is used when something is obvious because of the day that it occurs: traffic, for example would be busy around a football stadium on game day, given the day that's in it. On any other day the traffic would be unexplainable, but because its game day its obvious why there is traffic.
Buy our lists of British English, American English and Animal idioms in PDF format. They're perfect to use offline for reference or for use in class!
If you have a question about idioms, ask us about it in our Idioms Discussion Forum.
If you know of an idiom that you would like to be listed here, please use our online form to suggest an idiom.