What is "freshers' flu"

n. (context UK informal English) A cold or similar illness contracted by new students at a university, caused by gathering people (and the diseases they carry) from a wide variety of places in a confined area, allowing the diseases to spread to those without immunity.

Freshers' Flu is the name commonly given to a battery of illnesses contracted by new students during the first few weeks at a university, in some form; common symptoms include fever, sore throat, severe headache, coughing and general discomfort . The illnesses may or may not include actual flu, and is often simply a bad cold, but is so named simply due to alliteration. This is mostly a British term, and is rarely heard outside the UK and Ireland.