Meta: aliasing
Aliasing can refer to many things, but here it mainly refers to the jagged "stair-stepping" edges along curved and diagonal lines, usually an artifact of low resolution and older programs. Modern image editing programs often include binary brushes, which produce lines with an intentional aliased effect. The tag is generally reserved for posts that are noticeably aliased without zooming into the picture.
Note that aliasing alone does not mean that the post is also pixel art.
See also:
The following tags are aliased to this tag: aliased (learn more).
This tag implicates digital_media_(artwork) (learn more).