while(<DATA>){  #get a line of text from the DATA area, put it in special variable $_
    chomp;      #remove the "new line" character from the $_ variable
    #create a word array from the $_ variable
    #split with no options splits on whitespace by default
    @words = split;
    foreach $word (@words) {
        $hash{$word}++;  #increment the value pointed to by the $hash{$word} "key"
    }  
}