One significant difference is typically that the tag taxonomy is not centrally defined, but tags are agile and up to the end user. There is no configuration of properties, but simply when an account manager sees the need for tagging a record with e.g. “ERP” and “Priority” he simply writes “erp, priority” in a tag field.
The account manager can then use the tags for filtering or whatever need they have. It is fast, flexible and does not need preconfiguration. If the needs change the user can adopt it instantly. There could be thousands of tags.