The Free On-line Dictionary of Computing (30 December 2018):

Serial Line Internet Protocol

    (SLIP) Software allowing the
   Internet Protocol (IP), normally used on Ethernet, to be
   used over a serial line, e.g. an EIA-232 serial port
   connected to a modem.  It is defined in RFC 1055.

   SLIP modifies a standard Internet datagram by appending a
   special SLIP END character to it, which allows datagrams to be
   distinguished as separate.  SLIP requires a port configuration
   of 8 data bits, no parity, and EIA or hardware flow
   control.  SLIP does not provide error detection, being
   reliant on other high-layer protocols for this.  Over a
   particularly error-prone dial-up link therefore, SLIP on its
   own would not be satisfactory.

   A SLIP connection needs to have its IP address configuration
   set each time before it is established whereas Point-to-Point
   Protocol (PPP) can determine it automatically once it has
   started.

   See also SLiRP.

   (1995-04-30)