Portholes are windows in a vessel from which the crew can look outside, normally small and circular or hexagonal in shape, but can vary. Given the massive size of the JMC mining vessel Red Dwarf, it had a large number of windows, perhaps thousands.
Dave Lister and Arnold Rimmer had a porthole in their sleeping quarters aboard Red Dwarf. Starscapes could sometimes be seen through this porthole, especially in earlier series iteration of the bunkroom (Series I-II), where the porthole was more prominent. In bunkrooms of later series, the porthole windows are sometimes seen, but they are less prominent.
Fearing that Rimmer would destroy it out of jealously or fear of being replaced as ship hologram, Lister hid the hologram disc for his former crush Kristine Kochanski behind the solar panel outside their bunkroom porthole. ("Confidence and Paranoia")
The shuttle Starbug also had porthole windows, albeit much smaller. When Lister spent two centuries in Deep Sleep and awoke with amnesia, he looked at his reflection in the Starbug porthole window and asked himself, "Who the smeg are you?" ("Psirens") When the Dwarfers were being chased by the Simulant Trader in the SS Centauri, Cat suggested that they all moon out of the starboard portholes, since that would distract their pursuer. ("Beyond a Joke")
When the nanobot-resurrected crew, including Captain Hollister, were forced to flee Red Dwarf in an armada of shuttles, Rimmer found a way to save the ship. He then waved at Captain Hollister through a porthole (Hollister had previously locked the regular characters up in the brig) and Rimmer ordered Red Dwarf to fly on by the armada, as Hollister also looked on helplessly through his own porthole window. ("Only the Good..." extended ending)
One bunkroom the Dwarfers used had a giant window covering the entire wall. ("Back to Earth")
When Lister lost Starbug in a poker game with some BEGGs on their moon, he was was forced to fly back to Red Dwarf using the jet propellant from his space suit. He floated outside the bunkroom porthole, telling Kryten to let him in since he had forgotten his keys. ("Entangled")
When Lister got drunk and decided to give himself some "tough love", he left himself messages to watch when he was sober. One of those included watching his beloved guitar floating away from the porthole. ("Fathers & Suns")
When Rimmer used a Quantum Skipper to explore various dimensions of The Multiverse, he came across a version of Red Dwarf where the radiation leak never occurred and the ship had remained in the Solar System. Looking out of the bunkroom porthole window, Rimmer saw Earth for the first time in three million years. ("Skipper")
When Rimmer became the superhero alter-ego "The Mighty Light" and took a bomb safely out into space, the Dwarfers looked on through a porthole on G Deck, where they watched it explode. Cat had an uncharacteristic moment of thinking he may miss Rimmer, before Rimmer beamed back into the corridor. (The Promised Land)
- In the remastered episodes of earlier series, the porthole windows were given further digitally-created effects, such as additional passing planets and nebulas.