What, exactly, is the "early Church"? We use the phrase "The Early Church" all the time around here, which leads me to ask...  What exactly is "the early Church"?

The New testament Church is easy to define – the fellowship of believers that existed during New testament times.  But I've never come across a definitive date range for the "Early Church" or even a specific event or marker.

For comparison, the "Middle Ages" sounds like it might be a relative term, but the term "Middle Ages" refers to a specific time period – the 5th to the 15th century A.D.

Does "The Early Church" refer to a specific, commonly accepted time period in the history of the Church, or do we just use it to refer to "Sometime early A.D." with the definition of "early" being up to open interpretation?
Early church is not a technical term, so it can be used fairly loosely, but generally follows the history and writings of church leaders which are divided by time period into the Ante-Nicene era (prior to the council of Nicaea in 325AD) and the Nicene/Post-Nicene era, up to the scholasticism of the Middle Ages.

There is no period of the church which is devoid of meaningful history, but the early church is often cited as a form of implicit evidence to the earliest interpretations of various traditions, especially when the scriptures do not go into detail about how various doctrines and traditions were practiced. Yet Protestant bodies generally seek to denounce traditions, even early ones, when they are perceived to violate the teachings of scripture.