看语境如何，这里是在说医院吗？假设是在医院，ward就是指“病区”：
ward - block forming a division of a hospital (or a suite of rooms) shared by patients who need a similar kind of care;
bay就是多人病房（多人间），然后还有一些单人间（individual side rooms）。

ward=大型病房

大多数病区都分别设置有多人间病房和单人间病房。

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Note added at 22小时 (2017-03-27 14:01:26 GMT)
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Side rooms are normally used to nurse patients with particular clinical needs. For example, they may have an infection that could spread if they were nursed on the main ward, or they may need more frequent visitors which could be disruptive to the rest of the ward.
Side rooms are allocated to patients based on their clinical need. Patients can request to be moved into a side room if one is available, but it may not be possible to do so.
All beds on the main ward or in bays have curtains that can be pulled round to provide privacy. Do not disturb signs are hung on these curtains to ensure patients are not interrupted unnecessarily.
供参考！http://www.swbh.nhs.uk/patients-visitors/while-you-are-here/...

大区和边间病房

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Note added at 1 day1 hr (2017-03-27 17:50:41 GMT)
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边间单独病房

Ward 一般是指整個病房的通稱， 例如小兒科病房、內科病房…等等。 Bay則是一間病房中有多張病床， 可以同時有多位病人共用的房間。