A brooch was a type of jewellery.
Cameca gave the the First Doctor her brooch as he and his companions prepared to depart 15th century Mexico. (TV: The Aztecs) He wore it during his seventh incarnation (PROSE: White Darkness) and gave it to his granddaughter Susan Foreman as a Christmas present in his eighth incarnation. (AUDIO: Relative Dimensions)
The Sixth Doctor wore a cat brooch, occasionally touching, tapping, or rubbing it for good luck just before doing something particularly risky. (TV: The Twin Dilemma, Attack of the Cybermen, Vengeance on Varos, PROSE: Retribution, Time Wake)
Lagis acquired a brooch from Vadim and Nefta which, unknown to any of them, was made of metal from a Cyber Ship's Hapthoid reactor unit which was damaged when the Cybermen crashed in Klimtenburg centuries earlier. (PROSE: Plague of the Cybermen)
Missy told Clara Oswald that the brooch she had contained dark star alloy and was given to him by the Doctor when they were both still living on Gallifrey, regarding some event with the Master's daughter. (TV: The Witch's Familiar)