You can learn more about Keywords here. In this post I just want to cover how you would go about removing a Keyword from multiple contacts in bulk.
To find all contacts with a particular Keyword, you can use your Contacts by Keyword report. After filtering that report for your desired Keyword, you can then use the "Send to Search" button above it to send all contacts with that Keyword to your Advanced Search page.
From your Advanced Search page, place checks to the left of the names of those contacts from whom you want to remove the Keyword:
Then, click the Contact Options menu above your search results and select Bulk Actions:
Next, select Remove Keywords from the Bulk Contact Actions modal that appears.
After clicking Remove Keywords, you'll then see the Remove Keywords modal:
When you click inside the Keyword dropdown box here, the Keywords that display are those that your database users have established within your CRM that are currently applied to all of your selected contacts - you can learn more about adding Keywords to your database here.
To remove a Keyword from these contacts in bulk, just select it from this box and then click "Remove keyword". It may take a few moments to process, but once complete that Keyword will no longer be attached to the contact records that you selected.