In the context of snowsports, skis are two lengths of materal attached to the bottom of specially designed ski boots.
Modern skis are made from composite materals ranging from fibreglass to carbon-graphite and titanium. Newer skis incorporate microchips that help advanced fibres woven into the structure of the ski adjust its torsional qualities (rigidity).
In all cases, skis help distribute the skier's weight evenly to allow them to glide across the snow/ice. Most skiers also use stocks to help them maintain balance and control (and to give themselves a push when needed).
"I'm going to go skiing on my brand spanking new skis."