Historically, the term referred to the military special units controlled by the military intelligence service GRU, the Spetsnaz GRU. Currently, the term is also used to describe any special purpose units or task forces of other ministries (even the Ministry of Emergency Situations special rescue unit), also in some other post-Soviet countries.
Russian special forces skilled in highly-advanced CQB, and with the objective of getting behind the enemy lines and getting the job done quickly and efficiently.
Although they lost their fame at the end of the Cold War, they are still highly-capable soldiers trained on all aspects, including counterterrorism.