A laboratory was a place where scientists performed experiments. (AUDIO: Do No Harm) Some scientific equipment that might be found in a laboratory included Bunsen burners (PROSE: Time and Relative) cyclotrons, (TV: The Keys of Marinus) Petri dishes, microscope slides and Erlenmeyer flasks. (TV: The Pyramid at the End of the World)
During his exile on Earth, the Third Doctor had a laboratory where he could perform experiments to get his TARDIS working again. (TV: The Ambassadors of Death, The Three Doctors)
The Seventh Doctor had a laboratory aboard his TARDIS, near the TARDIS zoo. (PROSE: Echo)
On Moonbase Laika, the Second Doctor and Polly Wright worked in the medical unit's laboratory to cure a virus. (TV: The Moonbase)