According to the UiPath documentation, the Taxonomy component is used in the Document Understanding Template to define the document types and the fields that are targeted for data extraction for each document type. The Taxonomy component is the metadata that the Document Understanding framework considers in each of its steps, such as document classification and data extraction. The Taxonomy component allows you to create, edit, import, or export the taxonomy of your project, which is a collection of document types and fields that suit your specific objectives. The Taxonomy component also allows you to configure the field types, details, and validations, as well as the supported languages and categories for your documents.

Document Understanding - Taxonomy

Document Understanding - Taxonomy Overview

Document Understanding - Create and Configure Fields