An example of derp is what you'd say when you shut your locked door realizing that you've left your keys inside.
In the placeholder sense, often used with herp. Can be used like a noun or a verb or with various suffixes. Connotes that whatever it stands in for does not matter, and often that it is foolish or nonsensical.
(third-person singular simple present derps, present participle derping, simple past and past participle derped)