A screed is a long, boring speech or piece of writing with a bad attitude, like a rant. If you’ve had enough and you’re not going to take it anymore, go ahead and write an angry screed.
You can also call a screed a "harangue" or a "tirade." Another totally separate meaning of the word is “a construction tool made of wood or plaster that acts as a guide for the thickness of new plaster.” Screed originally meant "strip of cloth," like the kind you might write a long list on in the old days. Still, if you’re speaking or writing a screed, it’s like you’re reading a long tedious list.