Petechiae is the plural form of petechia, which is when bleeding from broken capillaries produce red or purple spots on the skin or the conjunctiva (the tissue inside the eyelids or that covers the white of the eye). The plural form, "petechiae", is almost always used rather than the singular form since a single lesion or petechia is often insignificant or unnoticed.
There are two ways to pronounce petechiae correctly and they are contingent on how you pronounce the final "ae" in the word. The first pronunciation of petichae is pih-tee-kee-ai, where the "ae" is pronounced like you would pronounce the letter "i". The second version of the pronunciation of petichae, which is also correct, is pih-tee-kee-ee, where the "ae" is pronounced with a second -ee sound. Generally, when pronouncing "ae" in British English, the -ee is prevalent, while in American English "ae" is usually pronounced with an "i" sound. However, this does not hold true for all words ending in "ae". With petichiae, you will find doctors and medical experts who pronounce petichiae differently, regardless of the form of English they speak.