What does & do at the end of a wc command?

Question

I am learning the bash environment and cannot understand what I get when running this command:

wc filename.txt &

It returns an array with a 1-digital integer and another integer, neither of them matches any other result I can get from wc commands (-l, -m, -w, -c). Besides the second integer is much bigger than for example the bytes counts. So I terribly wonder. I browsed forums and found some explanations on the multiple uses of the ampersand in a Unix/Linux environment, but there was nothing that I could relate. I don't need it, but I won't flush this mystery away, I wish to understand! Thanks

Answer 1

I imagine the integers you see are similar to this:

[1] 1830

& launches a command in the background, and the shell prints its job number (1) and process id (1830). On a longer-running job, you can use those two numbers to control its execution. See the JOB CONTROL section of the bash man page for more details.

Answer 2

An ampersand at the end of a WC command tells the shell to start executing the command in the background and to get ready for further command line commands.