Porn of mecha and robot characters, most commonly Transformers. It is used as a substitute for the word "porn" or the acronym "NSFW" to
tag art and writing.
In most valveplug, the word "interface array" is used to refer to the bot's genitals. "Spike" is used for "penis". "Aft port" is used for the
anus, whenever that applies. "Transfluid" is the most common replacement for
cum, and "lubricant" is self-explanatory. In some media, male bots (mechs) are equipped with both a spike and valve, while
female bots (femmes) have only a valve. However, in a
lot of media, everyone is a hermaphrodite.