What is High Crimes And Misdemeanors?

Legal Definition
The charge of high crimes and misdemeanors covers allegations of misconduct peculiar to officials, such as perjury of oath, abuse of authority, bribery, intimidation, misuse of assets, failure to supervise, dereliction of duty, conduct unbecoming, and refusal to obey a lawful order. Offenses by officials also include ordinary crimes, but perhaps with different standards of proof and punishment than for nonofficials, on the grounds that more is expected of officials by their oaths of office.
-- Wikipedia
Legal Definition
Such immoral and unlawful acts as are nearly allied and equal in guilt to felony, yet, owing to some technical circumstance, do not fall within the definition of felony. See 6 Conn. 415, 16 Am. Dec. 68.
-- Ballentine's Law Dictionary