what does its mean " single structuring element object" in IM2 = imclose(IM,SE) ???

IM2 = imclose(IM,SE) performs morphological closing on the grayscale or binary image IM, returning the closed image, IM2. The structuring element, SE, must be a single structuring element object, as opposed to an array of objects. The morphological close operation is a dilation followed by an erosion, using the same structuring element for both operations.

plz help to understand this line with any example.