You're all going to hate me for this... But what does it mean when someone asks what speed your lens is?

Please don't hurt me... I'm a mere amateur and trying to learn more. I always thought that speed referred to the shutter speed, but I was recently asked the question,"What speed is your lens?" and I had no idea how to answer and felt like a complete idiot. I was using a 17-55 mm f/2.8 canon lens... show more Please don't hurt me... I'm a mere amateur and trying to learn more.
I always thought that speed referred to the shutter speed, but I was recently asked the question,"What speed is your lens?" and I had no idea how to answer and felt like a complete idiot. I was using a 17-55 mm f/2.8 canon lens at the time if it matters...
Update: iansand- So, if I were asked the same question again regarding the same lens, my answer would just simply be the f number, 2.8?
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