Most of the Serial ports follow a standard called the RS-232 specification. RS-232 defines the meaning of the different serial signals and their respective pin assignments on a standard 25-pin (DB-25) serial connector.
DB-25 connectors can either be male, with the pins sticking out, or female, with matching holes. Often there is very small number marking for the pins or holes 1 through 25. The female connector is just a mirror image of the male, so that pins and holes match.
