Oh thanks Microsoft for using the same KQL identity for two unrelated items - the marketing department needs some fresh blood I think to come up with new names.
Anyway KEYWORD looks like a method of searching in SharePoint - according to the Docs reference here
Kusto is a Big Data query language used across products like Azure Data Explorer and Log Analytics to query data that in essentially in a tabular format. See here for details.
I wish Microsoft would stop using the same acronyms across totally unrelated products and services.