The following two characters are used to represent a carriage return.
Let's say foo.txt is transferred from a Windows system to a Linux system. Windows will end each line with a new line (\n) and carriage return (\r). On Linux, lines only end with a new line (\n), thus sometimes you may want or need to remove the carriage return (\r) from each line.
This command will remove the carriage return (\r) and redirect the results to a new file (bar.txt). This is the common approach because the -i option in sed may fail if the file did not have Full Control permissions on Windows.
sed 's/\r$//' foo.txt > bar.txt