A Latin plural is a plural formed according to the language rules in Latin. These were once most commonly found in Latin, though since its demise, not so much. Rather, what we're interested in is Latin loanwords (and loan phrases) in English.
Latin has a whole load of declensions, familiar o everyone who was subjected to it at school. Fortunately, most Latin loanwords in English are based on the nominative case, regardless of their case in English. Also, English loanwords follow natural gender, rather than Latin gender. The following declensions are reasonably common in English:
|Latin declension||Singular ending||Plural ending||Example(s)||Notes|
|Second declension masculine singular||-us||-i||
|Second declension neuter singular||-um||-a|
|Third declension masculine||-x||-ces||
|Third declension neuter||-us||-ora||
||Other examples? Third and Fourth declensions are very confusing|
||These are invariant|
Often a regularised form exists in English alongside the irregular Latin plural, so e.g. stadium has two plurals, i.e. stadiums and stadia.