Is serial port a 'male' or 'female'?
Solution 1:
That is a male serial connector. The big one is a female parallel connector. It used to be common to have both 25-pin serial ports (true RS-232 ports) and 25-pin parallel ports (smaller than the original Centronics parallel ports). The parallel ports were female, and the serial ports were male. This prevented accidentally connecting a cable to the wrong port.
This, of course, was not always the case, but it was a very common way of doing things.