Vim's "count" feature allows you to multiply or iterate a command by passing it an optional number. Questions about counting things should use the "counting" tag instead.

See :help count:

An optional number that may precede the command to multiply or iterate the command. If no number is given, a count of one is used, unless otherwise noted. Note that in this manual the [count] is not mentioned in the description of the command, but only in the explanation. This was done to make the commands easier to look up. If the 'showcmd' option is on, the (partially) entered count is shown at the bottom of the window. You can use <Del> to erase the last digit.