Please kindly help me understand the use of the term "śloka" in describing the contents of manuscripts, as in the case; "Extent of the manuscript: 300 ślokas." Clearly it does not denote only the verses in anustubh, because some works contain more or fewer verses than the extent given as such in mss catalogues, and even the contents of some prose works are introduced that way. 

Could it be the number of lines or complete sentences they refer to with the term śloka? 

Thank you.