Yes, is an arbitrary identifier between taiga and jira instance.
This tutorial explains better the process (I hope) https://developer.atlassian.com/cloud/jira/platform/jira-rest-api-oauth-authentication/ check especially step 2.
The public key should be configured in the Jira instance too with the consumer key when you create the “incomming link” (step 5 and 6 Migrate from Jira to Taiga).
- use your consumer key and your public key
