A sonic lance was a sonic device used primarily for cutting.
A small version once carried by the Sixth Doctor may have had chiefly medical applications, though this gave it secondary utility as a short-range weapon. Like the Doctor's sonic screwdriver, however, it had a variety of uses beyond the function its name conveyed. While it was seen to allow the Doctor to cut wires whilst repairing his TARDIS, it also helped the Cryon Flast heat up an explosive compound. (TV: Attack of the Cybermen)
The Sixth Doctor later carried a similar sonic lance while investigating into the affairs of the Paradise 5 staff and used it to unlock several doors aboard the station and tinker with the electronics in Peri's staff quarters. It also assisted in Peri's attempt to free the prisoners captured by Gabriel and Michael as offerings to the Elohim. (AUDIO: Paradise 5)
The Sixth Doctor used his sonic lance to blow up a door, in order to escape from the Rani. When Peri noted that it was in pieces, he said that he had a spare, and would be very careful not to break it. (PROSE: Something Borrowed)
Later, when attempting to free a trapped space whale being hunted by humans, the Sixth Doctor was able to essentially effect a limited "regeneration" on Peri's arm by "cellular reconfiguration". He later stunned their human captors by setting the lance to 3100 hertz at 800 decibels, allowing both him and Peri to escape back to the TARDIS. (AUDIO: The Song of Megaptera)
Sonic lances were also available commercially in some places. A larger version — in no way associated with the Doctor — was used on the planet Peladon in mining. Ettis tried to use this lance in his rebellion, having it taken to Mount Megeshra from where he planned to attack the citadel. Unbeknownst to Ettis, it had been rigged by the Ice Warriors with a self-destruct circuit preset by remote control if the lance was being used as a weapon. When he learned the lance had been stolen, Azaxyr activated the booby trap. The machine exploded when Ettis tried to turn it on, killing him. (TV: The Monster of Peladon)