Purpura – The term purpura is used to describe violaceous non-blanching hemorrhagic lesions larger than 2 mm (if smaller, it is called "petechiae". The can be flat or raised so they can be macules, papules, patches, or plaques. The term "palpable purpura" is used in association with indicate small vessel vasculitis.
Petechiae – Think of petechiae as a tiny, flat form of purpura. They are non-blanching reddish macules (they are flat) that are 1 to 2 mm in size. Petechiae occur from small capillary rupture into the skin. Often the result of infection or thrombocytopenia.
Ecchymoses (bruises) – Ecchymoses represent large extravasations of blood into the skin. They can occur from trauma or from underlying hematoma. Although the terms ecchymosis and hematoma are often conflated, it's easiest to think of hematoma is a pocket of blood collecting anywhere in the body, whereas eccyhmoses are restricted to the skin.