To slide means to move smoothly across a surface, usually without much friction or resistance. When you slide down a snowy hill on a sled, you glide along with barely any effort. Ice is famously slippery because things slide across it so easily. A hockey puck slides across the ice, and baseball players slide into bases, skidding along the dirt to reach the base before being tagged out.

The word can describe any smooth, gliding movement. Papers might slide off a tilted desk. A drawer slides in and out of a dresser. You might slide your chair closer to the table without picking it up.

A slide is also a thing: the playground equipment where you climb the ladder and whoosh down the slanted surface. Scientists use microscope slides, thin pieces of glass that hold specimens for viewing. A slide show displays a series of images, originally shown one at a time by sliding physical photographs into a projector, though today most slide shows are digital presentations.

When something slides into a worse condition, it gradually deteriorates: a student's grades might slide if they stop paying attention in class. If you let something slide, you're choosing not to make a big deal about it or enforce a rule strictly.