Final answer:
Eric Hickey defines a serial killer as one who commits methodical, patterned murders over a period of time, often with no clear motive and periods of inactivity between killings.
Step-by-step explanation:
The definition of a serial killer, according to criminologist Eric Hickey, characterizes a serial killer as an individual who commits a series of murders, typically with no apparent motive, and following a pattern or methodical practice. These individuals commit their crimes over a period of time, often eluding capture and can have periods of dormancy between their killings. Hickey's work in the field has contributed to the more formal understanding and profiling of serial killers, based on behavioral patterns and psychological analysis.