# BIO Tagging

> Source: https://sukruyusufkaya.com/en/glossary/bio-tagging
> Updated: 2026-05-13T20:58:56.589Z
> Type: glossary
> Category: dogal-dil-isleme
**TLDR:** A classical sequence-labeling scheme that marks entity boundaries with beginning, inside, and outside tags.

<p>BIO tagging is used especially in NER and related sequence-labeling tasks to make entity boundaries learnable. Through beginning, inside, and outside tags, the model learns which tokens belong to the same entity span. Although it appears simple, it is one of the most important representations for exposing span structure to a model. Tagging quality directly affects downstream performance.</p>