Is DB-25 port Serial or Parallel?

Is DB-25 port Serial or Parallel?

A DB-25 connector could be serial port or parallel port or something else.
A DB-25 connector is a generic connector.
It is not exclusively used by just one interface (like HDMI or USB connectors are).

On a modern PC, a DB-25 (especially a female connector) is typically associated with a parallel (aka LPT) port.
On older computer and telecommunication equipment, a DB-25 connector is typically a RS-232 serial port.

Prior to the mid-1980s, RS-232 ports typically used DB-25 connectors.
Printers used RS-232 interfaces and/or custom interfaces.
One of those interfaces, a parallel interface using a 36-pin connector developed by Centronics, became an industrial and then an IEEE standard.

When IBM introduced its PC, it substituted the large Centronics connector with a slimmer female DB-25 for the LPT port. The female DB-25 connector was typically used for DCE RS-232 ports (e.g. a phone modem), and this was a new application for that connector. The RS-232 port(s) on the IBM PC used male DB-25 connector(s).

When IBM introduced its second-generation PC/AT, in 1984, IIRC it substituted the large male DB-25 connectors for RS-232 ports with "DB-9" (actually a DE9) connectors that today's users associate with "serial" ports. The parallel LPT port continued to use the female DB-25 connector.

The connectors themself arn't actually specific to a protocol - It simply refers to the number of pins and that its sub miniature. You could in theory wire up any suitable connector to the right electrical connections and to use it.

In most systems I've seen, serial ports had 9 pins (since they didn't implement the whole 25 pin standard). I could also have, in theory the same 9 pins on a mini DIN connector or used the same 9 or 25 pins for another protocol.

On the other hand, printers often had a centronics port rather than a DB25, and once again, the physical connector simply had to support the minimum amount of pins the electrical standard needed.

At the end of the day the smart thing is to check before you plug anything in ;p