"key segments" is correct and can be used in written English.
You can use it to refer to important parts or components of something. For example, "This report outlines the key segments of the new market."
The A.S.P. arena has three key segments.
Key segments came from her latest album, Encore, which features songs from Broadway, sung in duets with movie stars.
Despite its many marques, VW is absent from key segments, such as the compact multi-purpose vehicle (MPV).
And yet, there was no getting around the evidence that the stock-market correction coincided with an actual slowdown in some key segments of the technology industry.
"All the key segments included in this data are dramatically outperforming recent trends," said Jonathan Banks, senior director editorial and data serves for NADA Used Car Guides.
The decision to run away from a President who remains popular within his party and with key segments of the electorate is inscrutable, but no more so than the state of affairs that facilitated it.
For example, single mums are a key segment for the US food producer Oscar Mayer.
In this way, retailers can tap into the key segment of consumers who buy on impulse.
But Gora shot an eight-panel sequence of the home run, its key segment reproduced many times.
Artie Bulgrin, ESPN's senior vice president for research, said this year's declines were accelerated by a key segment of viewers focused on the war in Iraq.
In eukaryotes, a key segment is the TATA box, a TATA sequence approximately 30 nucleotides upstream from the transcription start site.
