Best guess, its the client ID that vendors use to access Google API
s.
A quick search reveals man similar, and I do think this is related to vendors capability to connect from their (mass) devices using API provided by Google.

http://www.google.com/m/search?client=ms-samsung-bada
http://www.google.com/m/search?client=ms-opera-mini
http://www.google.com/m?client=ms-unknown
http://www.google.com/m/search?client=ms-nokia
http://www.google.com/m/search?client=ms-ucweb
http://www.google.com/m/search?client=ms-nokia-meego

are a few