What is Hypervalent species or compounds?

The compounds or ions which doesn't follow octet rule inspire of that contains more than eight electrons and also stable called Hypervalent species.

For examples XeFe₂(10e), XeFe₄(12e), SF₄(10e), SFe₆(12e), IFe₇(14e), I₂Cl₆(10e), TeF₅(12e) etc

Hypervalent species may act as Lewis acid but not always.