(noun) Colloquial, generic term used by birders to describe small, difficult to identify birds such as relatively unremarkable sparrows, warblers, wrens or finches. Poor light, active behavior and other conditions can keep clear field marks from being seen, further complicating identification.
While this term is not official for any ornithological text, it is widely known among birders and can be used either wistfully or dismissively. When used wistfully, the birder often wishes to identify the birds in question but is unable to do so despite making the effort. When used dismissively, the birder prefers not to spend the time to identify small, plain birds that have likely been seen before.