Slang term, originating in Somalia, for consumer or civilian vehicles(traditionally light pickup trucks) that are modified for use in combat.
The modifications usually include adding improvised armor to vulnerable areas, and adding a turret for some type of mid-sized weapon (i.e. machine guns or recoilless guns). While technicals are usually less effective than a custom-designed vehicle with similar weaponry - let alone heavier vehicles - they allow guerillas, mercenaries, militias, and other poorly-funded combatants to put highly mobile gun turrets onto the battlefield at a reasonable cost.
Apparently, the term 'technical' originated from the humanitarian organizations that operated in Somalia in the early '90s, before the ill-fated UN/US operation there. Faced with the threat of various warlords and bandits attempting to steal food and medicine, the humanitarian groups soon learned to hire mercenaries of their own to serve as bodyguards. Possibly to avoid embarrasing questions, the groups listed the fees and expenses of hiring the mercenaries as 'technical expenses.' The term 'technical' stuck, for both the mercenary bodyguards and their improvised vehicles of choice.