Lifeless
The Lifeless are a specific type of awakened creature from Warbreaker.
When an Awakener infuses a skeleton or corpse of a living being (preferably a human) with a Breath, as well as with a specific mixture of alcohol, that creature then becomes animate without becoming fully alive. This creature is then able to follow specific commands much like any other Awakened creation.
However, Lifeless differ from other awakened objects in several ways. Firstly, the Breath used to animate them cannot be reclaimed by the Awakener. Secondly, they are much more flexible and intelligent in obeying orders; in universe, this is ascribed to the fact that they have a brain and are therefore less reliant on the cognitive impulse from the awakener to determine their actions. Thirdly, they can be given further commands, or have their previous commands rescinded, without an infusion of more Breath. A Lifeless will remain animate, and therefore useful, for as long as the body remains in good condition.
There are also hints in the books that Lifeless may not be completely without awareness or agency. The Lifeless known as Clod seems to help Vivenna beyond his commands on multiple occasions. It is confirmed in the Annotations that the Lifeless do retain a certain amount of self-awareness after their awakening, although the implications of this are as yet unexplored.
Lifeless are useful due to the fact that they do not feel pain as soldiers and require very little maintenance and no food. Furthermore, the Lifeless retains a measure of the skill that it possessed when alive, thus making it exceedingly economical to reuse one's dead soldiers as lifeless, thus saving money on training costs as well as upkeep.