untagged

Untagged is an adjective describing something that has not been tagged, labeled, or annotated with metadata. The term is used across several domains to indicate the absence of tags or identifiers that would otherwise categorize, identify, or describe the item.

In computer networking, untagged frames are frames that carry no VLAN tag. Switch ports can be configured as untagged members of a single VLAN (an access port) or as tagged members (a trunk port). The port’s default VLAN is called the port VLAN ID (PVID); frames arriving untagged on a port are assigned to that VLAN. On trunk links, most frames are transmitted with VLAN tags corresponding to their VLAN, while the native or untagged VLAN traffic may be sent without a tag.

In data processing and machine learning, untagged or unlabeled data lacks target labels. Supervised learning relies on labeled examples, while unsupervised and semi-supervised approaches work with untagged data or only a subset of labeled data. The presence or absence of tags affects data preparation, model training, and evaluation.

In media and social platforms, untagged generally refers to content without user tags or metadata. Photos or posts may be untagged if they do not include person tags, or if metadata such as keywords, author, or location is missing. In music files, ID3 or other tags may be absent or incomplete, leaving a track untagged.

See also: tagging, metadata, VLAN tagging, unlabeled data.