You're seeing just the function
update, go back to SlackWeb.Usergroups module for more information.
Update an existing user group
usergroup- The encoded ID of the user group to update. ex:
channels- A comma separated string of encoded channel IDs for which the user group uses as a default.
description- A short description of the user group.
handle- A mention handle. Must be unique among channels, users and user groups.
include_count- Include the number of users in the user group. ex:
name- A name for the user group. Must be unique among user groups. ex:
My Test Team