Each operator can have a set of text strings that are its "tags". For example, tags can be used to categorize and gather components of a certain user-defined classification, such as 'color filter' or 'audio effect'.
You can put tags on operators in the UI at the top of the Parameter dialog, and via python using, for example
node.tags = ['tag 1', 'tag 2']
You can search for operators with specific tags using
OP.findChildren() method and the OP Find DAT.