(interrogative) What, of those mentioned or implied.
The/Any ... that; whichever.
(relative, formal outside certain phrases) Designates the one(s) previously mentioned.
(interrogative) What one or ones (of those mentioned or implied).
The/Any ones that; whichever.
(relative) Introduces a non-restrictive relative clause giving further information about something previously mentioned.
(relative, sometimes proscribed) Introduces a restrictive relative clause giving further information about something previously mentioned. (see usage notes)
(relative, chiefly archaic) Used of people (now generally who, whom, that; which remains possible with words also referred to by it like baby, child).