"defining impact" is a correct and usable phrase in written English.
You can use it to describe a profound change or influence that something has had. For example, "This ruling has had a defining impact on the way the industry is regulated."
"Invasion ecology is making real progress with defining impact and characterizing risk," write Julie Lockwood of Rutgers University, Martha Hoopes of Mount Holyoke College, and Michael Marchetti of California State University, Chico.
But the show's defining impact was not financial; it was subliminal.
Mr. Sondheim, the Tony Award-winning composer and lyricist of musicals including "Company," "Follies" and "Sweeney Todd,", said in a statement that teachers could have a defining impact that ought to be recognized and rewarded more fully.
But Romney's current predicament and challenge is such that it's not difficult to see how the outcome of the Republican debate in Jacksonville this evening could have a defining impact on the outcome of next week's Florida primary and fundamentally shape the road forward for Romney and his opponents.
Yet a closer look at the Canadian experience reveals that public property in Canada's cities is abundant, and that public landowners often have a defining impact on urban development outcomes.
The temperature level has a defining impact on the efficiency of the distribution through heat losses and it improves the potential for integrating new sources of heat into the system.
Hinting at the continuing nature of the analysis, the report noted, "Film review continuing to better define impact area".
We define Impact as the normalized difference between Alignment and Alignment∗.
Upon the determination of the initial velocity of beam and the defined impact loading history in Fig. 12, a nonlinear dynamic time history analysis was conducted.
Next, model elements which are directly or indirectly impacted by the changes (i.e., may undergo changes) are determined using formally defined impact analysis rules (defined with the Object Constraint Language).
Another way to define "impact" is awareness.
