I'm active on many discussion fora, but I see that people more often use the form forums.
Are both forms correct and adequate?
If so, why are there two forms for the plural of such a short word?
Learn English – Which is the plural of “forum”: “fora” or “forums”
latinplural-formsword-form
Related Solutions
Both are correct, though there are some specific usages as pointed in another answer; Google Ngrams suggests that indices is slightly more used than indexes.
For American English we have (in both charts, indices is blue and indexes is red):
For British English we have:
If both words 'cats' and 'dogs' are plural then 'A' option is correct!
A - "Cats and Dogs"; this shows more than one cat and more than one dog.
While:
B - "Cat and Dogs"; this shows single cat and more than one dogs.
Best Answer
Although the proper Latin plural would be fora, forum has been adopted into the English language--and in most cases follows the rules of English pluralization. Similar changes can be seen with the adoption of other words like octupus (the proper plural would be more like octopedes, but in English we usually say either octopi or octopuses).
The current entry from the Oxford Dictionary says:
Since you're talking about online discussion boards, I would use forums instead of fora when you are talking about more than one. An English speaker might understand fora, but it wouldn't come as naturally.