not very passive, but in some cases blog posts can be popular for years and therefor generate revenue for years (but not in many fields/topics)
-> kind of passive in the long run
-> kind of passive in the long run
For example, I was blown away by how useful & accurate this guy's medium blog was for setting up apache.
https://medium.com/@JohnFoderaro/how-to-set-up-apache-in-mac...
(just used this for a class, I'm not pushing anything for anyone)