To monitor; to track or record; to understand or follow.

(Internet) The use of code associated with a single pixel tag (invisible to the user) to monitor the activity of the user, especially his use of advertisements

A lightweight shoe with spikes screwed into its bottom in order to maximize traction (and therefore performance) when running or jumping.

(of a railway) having a single set of lines so that trains can run only in one direction at a time; single-track / limited to one idea or thought

railroad track, railway track / (topology) A set of curves lying in a surface, meeting one another at their respective endpoints in a specific way that resembles railroad tracks

present participle of fast track

(Australia, Canada, New Zealand, US) Sweatpants.

(rail transport, US) A pair of formed steel rails, separated and supported usually on wooden or concrete ties or sleepers, forming a track along which flange-wheeled railroad vehicles may travel.

(softball, baseball) The dirt or other material on the edge of a baseball or softball field that warns a player that he or she is approaching the fence, especially the portion in the outfield.

(sports, chiefly racing) The lane or track nearest to the interior. / (figuratively) Any advantage.