Keyword understanding

Hi guys,
I got a few question for a better understanding of keywords.
What delimites keywords in the title?
Let say i have 2 keywords "cats" and "dogs".
a- 1 keyword wold be: cats and dogs
b- 2 keywords would be: cats - dogs or cats | dogs .Delimitations beeing "-" and "|"
c- cats-dogs is this one keyword?

I think it's one keyword with two words. and the character between two word except word is not going to give you much effect

If you've meant both cats and dogs in the context, your keyword is going to be "cats and dogs". If it is supposed to be one or another or both you should most likely use 2 keywords "cats" and "dogs". On youtube I would go for the last one in any situation.