From The Free On-line Dictionary of Computing (19 January 2023):
count
<programming> One of the built-in aggregate functions in
relational database systems, that returns the number of rows
in a result. The argument to the function is nearly always
"*", e.g.
SELECT COUNT(*) FROM books
which returns the number of rows in the "books" table. If,
instead, we say
SELECT COUNT(publisher) FROM books
then only rows with a non-null value in the "publisher"
column will be counted.
(2010-09-26)