This is in reference to Shopify, Square, Twitter, Facebook's recent announcement.
Thanks
WFH just means you're at home. Usually there is a policy about it, e.g. "only 1 day a week" or "3 days a month" or "with Mgmt approval" etc.
Flexible is just a WFH policy that's a lot more open. I'm 100% remote but my coworkers are local and are obligated to go into the office at least once a week, sometimes more for big meetings or sensitive discussions.
Permanent work from home & remote are more or less the same thing. There may be a contextual difference, depending on if there are expectations that you're near an office, or if you can just piss-off to Estonia or Indonesia or wherever. I'm remote, but with a clear expectation that I stay in country, mostly for security and access reasons.
OTOH, I knew a Swedish dev who rented a VW Van and packed in spare batteries, a mattress, and good satellite internet, and then worked remotely driving across Australia -- that's about as remote as it comes.