COB stands for "close of business" or "close of play" and refers to the end of a business day. It is typically around 5:00 or 6:00 pm, depending on the industry and location. COB is used in business communications to set a deadline for a task to be completed by the end of the business day. COB can be used interchangeably with end of business (EOB), end of day (EOD), end of play (EOP), and close of play (COP).

EOD, on the other hand, stands for "end of day" and refers to the end of a business day. It is also used to set a deadline for a task to be completed by the end of the business day. EOD and COB are often used interchangeably, but EOD can also refer to the end of a calendar day.

In summary, COB and EOD are both used to set deadlines for tasks to be completed by the end of a business day, but COB specifically refers to the close of business or close of play, while EOD refers to the end of the day more generally.