A casting vote is typically by the presiding officer of a council, legislative body, committee, etc., and may only be exercised to break a deadlock.
For example, the speaker of the British House of Commons (a position whose functions and conventions of operation inspire similar roles in several other nations using the Westminster system) is expected by convention to follow Speaker Denison's rule (i.e., to vote to allow further discussion, if this is possible, and otherwise to vote in favour of the status quo).
Robert's Rule of Order Newly Revised (12th Edition, 2020) does not include the concept of a casting vote.
Some legislatures have a dual approach; for example, in the Australian Parliament: The same arrangements as in Australia exist with respect to the speakers of the Canadian House and Senate.
Pursuant to Article I, Section 3, Clause 4 of the United States Constitution, the vice president has a casting vote in the Senate, in the event of a tie.
This type of casting vote does not now exist; after the 1866 Helston by-election, Parliament allowed candidates who tied to both be elected.
[4] Ties in United Kingdom elections are now broken by drawing lots, using a method decided upon by the Returning Officer.
Ties in Nova Scotia, Prince Edward Island, and the territory of Yukon, are now broken by lots as they are in the United Kingdom currently.