Preterism is a theological construct that views the majority of biblical prophecies as having occurred in the past.   Preter is Latin for past.  The chief focus of preterism is the millennium and the subsequent millennial reign of Christ.  A preterist is someone who holds this view. 

preterist \Pret"er*ist\, n. [Pref. preter- + -ist.] 1. One whose chief interest is in the past; one who regards the past with most pleasure or favor.

2. (Theol.) One who believes the prophecies of the Apocalypse to have been already fulfilled. --Farrar.

Source: Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.

A necessary corallary of preterism is the view that the Old Covenant is just that - old.  It has been fulfilled and thus abrograted by it's fulfillment in Christ.  Preterism stresses the importance of the nature of Christ, His Redemptive Work and the Inauguration of the New Covenant and subsequent inclusion and ingathering of the Gentiles.

An unnecessary inference from preterism is the view that Christ was not raised from the dead bodily or that He will not Return for His own physically.

What is millennialism and what millennial views are there besides preterism?

Millennialism (often referred to as chiliasm) is the doctrine of Christ's expected return to reign on earth for 1000 years.  There are 3 basic views: preterist, presentist, and futurist.

These 3 views are developed within various millennial systems. 
The major 3 are defined below.