Something that is made and/or used by a human. Artifacts include tools, containers, and food scraps (such as animal bones and corn cobs). Artifacts also include things that are leftover when a person makes something. For example, to make a stone arrowhead (also called a "projectile point"), a person had to chip small flakes of stone off of a larger stone to get the right shape. The small flakes are artifacts that help archaeologists understand how the arrowhead was made.
Technically, artifacts also include things that people build, such as houses and fire hearths. But archaeologists usually use the word "artifact" only to describe things that can be picked up and carried away.