Tracking is a canine sport in which the dogs follow the path of a human starting with one object with the person's scent (e.g. a glove) and ending at the scented item (e.g. the other glove).
Scent work or nose work is a sport in which dogs are taught to identify specific scents (e.g. anise or birch) and locate them in various hidden places, while ignoring other scents and distractions.
For many dogs this is a way for them to use their natural drive to find and follow scent in a safe, constructive, and fun game.