If I have the keywords "french, toast" will french toast automatically be a keyword applied to my site? Or does it need to be specifically stated. "french, toast, french toast"
According to the HTML5 spec, the value "must be a set of comma-separated tokens, each of which is a keyword relevant to the page".
In the example you can see that a token can include a space (in "type face"):
<meta name="keywords" content="british,type face,font,fonts,highway,highways">
So for this example the algorithm would add the following items to the keywords list:
Strictly speaking, these are not keywords:
So yes, you'd have to explicitly state combinations of keywords (if they make sense). "Stack" and "Overflow" is not equivalent to "Stack Overflow".
However, depending on the implementation of the consuming user-agent, this might not be needed, as some user-agents will probably throw all keywords into a basket anyway.