Exactly what they appear to be; moderately heavy hunks of solid metal 1 lists in the hope of eventually lifting heavier hunks of metal. Can be delivered to Stanford campus or picked-up in Mountain View. $6 for a single 15lb. $10 for both fifteen pound. $8 for a single 20 pound. $13 for both 20 pound.
It's a piece of metal you lift up and down. :P I don't have photos at the moment, as I don't have a camera. For reference, it's this guy: https://www.amazon.com/CAP-Barbell-Dumbbell-Single-30-Pound/dp/B0012718T2/ref=sr_1_6?s=sporting-goods&ie=UTF8&qid=150519XXXX&sr=1-6&keywords=cap%2Bdumbbell&th=1