A tool is any physical item that can be used to achieve a goal, especially if the item is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tool use by humans dates back millions of years, and other animals are also known to employ simple tools. Tools that are used in particular fields or activities may have different designations such as "instrument", "utensil", "implement", "machine", or "apparatus". The set of tools needed to achieve a goal is "equipment". The knowledge of constructing, obtaining and using tools is technology.
Anthropologists believe that the use of tools was an important step in the evolution of mankind. Humans evolved an opposable thumb — useful in holding tools — and increased dramatically in intelligence, which aided in the use of tools. Because tools are used extensively by both humans and wild chimpanzees, it is widely assumed that the first routine use of tools took place prior to the divergence between the two species. These early tools, however, were likely made of perishable materials such as sticks, or consisted of unmodified stones that cannot be distinguished from other stones as tools. Stone artifacts only date back to about 2.5 million years ago. However, a 2010 study suggests the hominin species Australopithecus afarensis ate meat by carving animal carcasses with stone implements. This finding pushes back the earliest known use of stone tools among hominins to about 3.4 million years ago.