What are the backslashes that are use in turbo C?

Backslashes are used to mark the start of an escape sequence which can be used within character arrays (strings) or as a single character. Thus the escpae sequence '\t' is the TAB character, '\n' is the newline character and '\r' is the carriage-return character. To print a literal backslash, you use a double backslash, '\\'. Note that the backslash and the escaped character that follow are treated as being one character (two bytes of UNICODE, or one byte of ASCII).
This convention is not unique to Turbo C. It was inherited from ISO C.