Final answer:
The medical term for the presence of ecchymosis is 'ecchymosis,' and its plural form is 'ecchymoses'. This condition is caused by bleeding underneath the skin due to vessel injury.
Step-by-step explanation:
The medical term for the condition defined as the presence of ecchymosis is ecchymosis itself, and its plural form is ecchymoses. Ecchymosis refers to a discoloration of the skin resulting from bleeding underneath, typically caused by bruising. The blood from the injured vessel leaks into the skin and mucous membranes, leading to this appearance. An injury such as a blood vessel being severed can cause such bleeding. The condition often presents as larger purple or blue patches that are sometimes confused with petechiae, which are smaller red or purple spots resulting from blood leaking out of damaged vessels.