A stretch of highway 401 in Toronto between Keele and Jane streets. The 401 is the major east-west route through Toronto. This freeway features a set of express lanes and a set of collector lanes running in parallel in each direction (east and west). At the basketweave, interchange lanes allow drivers in the express lanes to move to the collector lanes, and vice versa. This is accomplished with a flyover/under pattern where the interchange lanes cross above/below each other, allowing traffic to merge both ways without adverse impact on driving speeds. Viewed from above, the pattern is pleasantly like that of a woven basket. Viewed from the highway, it's just more road, and you tend to be focussed on completing your lane changes, rather than the esoterica of highway design.
The name is used as a shorthand for this area during traffic reports, as in:
Traffic continues slow through the basketweave in both directions.