"Unique units" in the free-to-play game C-evo are a handful of units each of which is initially produced by only a single nation. Examples are the Roman ship "Liburna", the Scots "Highlander" (for the Scots tribe that was available for version 1.1.1), and the Japanese "Samurai" (which may have two variants).
Because of the "Do It Yourself" nature of all units in C-evo apart from the predesigned Special Units and the predesigned basic Militia, the concept is of much less significance in C-evo than in the Civ Series games that make considerable use of the idea. Any nation can design units that have exactly the same name and attributes as any "unique" unit. In fact, if one nation produces its "unique unit" (such as the Samurai) other nations that later produce a unit having the same attributes may find the same name being applied by default. A human player can then rename his or her own unit (on its creation or by right-clicking the units menu), and it is useful to include the unit's distinctive attributes by using a name such as "18/6/2.5-Cavalier".
Players with some computer proficiency may be able to modify files to produce their own unique units that cannot be copied.