what are nested tables?

[PotsNPans]

What exactly are "nested tables?" I've heard these are good to avoid when designing a website, but I'm not clear on how they differ from regular tables.

[suwunk]

Hence, nested tables. This technique means that tables can be placed within tables. Tables could then be placed within those tables, which would create a 3rd level of nesting, but at this point we won't go into anymore complexity than is necessary.
Nesting HTML tables tutorial (http://www.designplace.org/tutorials.php?c_id=5&page=1)

[kabonm]

Hence, nested tables. This technique means that tables can be placed within tables. Tables could then be placed within those tables, which would create a 3rd level of nesting