tracker

noun

• 1a person who tracks someone or something by following their trail: he operated as a police tracker in the Halls Creek area
• a device that follows and records the movements of someone or something:electronic trackers are now showing ornithologists where the birds go

• 2 Finance an investment fund which aims to follow in value a stock market index or group of indexes.
• a mortgage or savings product whose interest rate aims to follow a particular public interest rate.

• 3 Music a connecting rod in the mechanism of an organ.