The article links to an explanatory page in the very first paragraph after the lede.

Vector tiles serve up maps as vectors: points, lines and polygons. They store geographic data (like what makes up OpenStreetMap) in a format that allows for dynamic styling and interactivity. For users, vector tiles will mean a new, modern-looking map style with seamless zoom on openstreetmap.org, the map can be updated more quickly when data changes, and it should perform better for users.