A laser was, in a description posited by Leela and approved by the Fourth Doctor, a very powerful light. (TV: Horror of Fang Rock) Many lasers were harmless and used in some games, (TV: Warriors of Kudlak) but others were used as deadly weapons. During their campaign to recruit warriors, the Uvodni utilised harmless laser weapons in their interactive laser-tag game Combat 3000. However, on board their ship, the Kudlak warriors carried deadly blaster rifles that fired a yellow laser burst.
The parallel Torchwood developed laser weapons, which destroyed Cybermen and could blast through a Dalek's shield. (TV: Doomsday) These weapons were later upgraded, to the point that they could destroy Daleks in one shot. (TV: The Stolen Earth)
In the video game Attack of the Graske, which this wiki does not consider to be a valid DWU source as it has multiple endings which we cannot qualify through any mechanism which one is the "correct" or "canonical" one, Graske on the planet Griffoth were shown to be armed with tiny laser pistols which fired purple blasts to combat intruders.