It understands it precisely as perldoc -f sleep explains. Now, is there anything you couldn't understand in it?!? Or is it the underscore, what that bothers you? If so, then it has nothing to do with sleep itself. It's just a number literal, and you can put underscores in them to improve readability at your will. 
$ perl -le 'print for 1_000_000, 0x1_000_000'
1000000
16777216

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In reply to Re: perl's sleep function by blazar
in thread perl's sleep function by jesuashok

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