A slalomist is a person who skis or snowboards in a slalom race, going around poles or gates.
Being a slalomist means being good at skiing or snowboarding and being very fast and agile.
Examples:
The slalomist went very fast down the mountain.
She is a very good slalomist.
The slalomist skied around the poles.
The slalomist won the race by going very fast.
The slalomist was like a rocket on the snow.
I want to be a slalomist when I grow up.