SD card 'overlay'

I've been dealing with unix/linux filesystems since 1985 and I never saw the term 'overly' applied. I know that a whole filesystem can be replaced just by mounting a different device on the mount point, including /. Since I've been using the Yun, I keep seeing references to the 'overlay' provided by the SD expansion. Can anyone clarify exactly what overlay means as to the procedure of expansion with SD?

heggood:
I've been dealing with unix/linux filesystems since 1985 and I never saw the term 'overly' applied. I know that a whole filesystem can be replaced just by mounting a different device on the mount point, including /. ...

1+

Overly/Root mount at openwrt:

I prefer pivot root "/" than pivot overly "/overly" personally.

I think Puppy Linux uses a similar overlay system - you may find something useful (or interesting, or both) on the website.

...R

Robin2:
I think Puppy Linux uses a similar overlay system - you may find something useful (or interesting, or both) on the website.

...R

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