You will have encountered abbreviations derived from Latin expressions. Here's what they mean, first as spelled out in Latin, and then (after a double-dash) as translated into English.
aff. - affinis -- having affinity with but not identical to
auct. - auctorum -- of authors [written like that by various authors]
ca. - circa -- about [refers to dates]
cf. - confer -- compare with
c.v. - curriculum vitae -- (curriculum of life), or resume
[it is curious that we have to give the nearest English equivalent
as a French word (résumé), which is spelled in American
English resume. Some people call a c.v. "a vitae", but
vitae means "of life"].
e.g. - exempli gratia -- for example
et al. - et alii -- and others
etc. - et cetera -- (and the rest), and so on
ex. - exemplar -- example or specimen [the plural is written exx.]
ibid. - ibidem -- from the same place
id. - idem - the same
i.e. - id est -- that is (to say), or in other words
in coll. - in collectionem -- in the collection [usually followed by the name of a collection or museum]
indet. - indeterminans -- unidentified
in litt. - in litteris -- in correspondence
leg. - legit -- he, she, or it collected
loc. cit. - loco citato -- in the place [work, paper, etc.] cited
n.b. - nota bene -- take good note
op. cit. - opere citato -- in the work cited
p. - pagina -- page [singular; plural is paginae, abbreviated pp.]
s.l. - sensu lato -- in the broad sense
sp. - species -- species [singular; plural is species, abbreviated as spp.]
sp. nov. - species nova -- new species [singular; plural is species novae, abbreviated as spp. nov.]
ssp. - subspecies -- subspecies [singular; plural is subspecies, abbreviated sspp.]
s. str. - sensu stricto -- in the strict sense
q.v. - quod vide -- see (for which, see)
viz. - videlicet -- namely