What do medical terms ending in the letter combination ae signify?

The medical terms that ends with ae letter combination shows that it is the plural form of the term.
for example bulla is a medical term which is used for blisters which are filled with fluid, when there is more than one bulla we use the word bullae, that is the plural form of the word bulla. 

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We can use solar powered cars or ride bikes instead of cars that burn fossil fuels