Lapsus calami—from the Latin "lapsus" (lapse or slip) and "calami" (of the pen)—literally means a "slip of the pen". It's what we refer to these days as a "typo".
Normally enclosed in brackets, lapsus calami follows words or names, particularly the scientific variety, that have been rumbled as misspellings in the literature and turn out to be synonymous with something else. For example; Yunnanosaurus = Yuannanosaurus (lapsus calami). Personally, we prefer "academicum hallucinatus" (an academic made a mistake).
Lapsus calami means the same as Lapsus plumae (a slip of the plume), referring to the most ancient of pens; the quill.
