Purchase Orderは
略すと　
PO
P.O.
P/O

どれもok?

またP/Oの間のスラッシュは何ですか？

複数形になるとPOs ですか？

See a translation

@Mirai55 All of those are valid ways to abbreviate Purchase Order in my opinion. “P/O” and “P.O.” would be more standard but “PO” could show up especially in more casual writing.

Personally I would use P.O. though and that is probably what the majority would usually do.

The slash “/“ functions the same way as the “.” in this case. It is less common to use, though you see it in abbreviations like “w/o” “w/“ “n/a” so it is by no means rare.

The only difference is you would only use “/“ in the middle - never at the end. So “purchase order” could be “P/O” or “P.O.” but “December” would only be written as “Dec.” and not “Dec/“


edit:
And yes for a plural of either one, you would add a lowercase “s”