What Is Piracy?
Colloquial Definition
When you obtain a copy of some media - could be songs, movies, TV shows, books, or games - through unofficial means, we say that you have pirated it. "Sailing the high seas" and "earning your sea legs" are common euphemisms for piracy.
The most common justification people for pirating something is being broke, and a lot of such people move away from piracy once they are able to pay. Part of the reason to pay when able is that people are (somewhat justifiably) afraid of accidentally downloading malware from piracy websites or torrents.
Legal Definition (In Most Jurisdictions, I Think?)
Legally, piracy is the act of distributing media to others (not obtaining media for yourself) through means that you are not authorized to do under the copyright attached to said media.
While creative work typically enters the public domain after 70 years, many jurisdictions allow it to be fast-tracked for media that is no longer sold legally.
More on this later.
More Justifications For Consuming Pirated Content
Refusal To Financially Contribute To Creators
Sometimes, enjoyable media is created by problematic people, and one may choose to consume (either to enjoy or to critique) said media while not contributing to the revenue stream. I do this with the youtuber exurb1a, watching his videos in a way that doesn't increment the view count.
Convenience And Service Quality
"Piracy is almost always a service problem and not a pricing problem" - Gabe Newell
Some paid streaming services have ads. Netflix blocks 4K content on 4K smart TVs. Some streaming services (youtube included) require the app to have been online recently to play downloaded media. Netflix anime don't even have accurate subtitles. Some games require an internet connection to play single-player. Some media is region-locked.
All of this makes for a crappy experience, and some people may choose the hassle of downloading a pirated copy instead.
Ownership And Archival
"If buying isn't owning, then pirating isn't stealing" - Linus Tech Tips? Louis Rossman? I couldn't track down the owner.
When you purchase a DVD with a game or a movie on it, you own that copy and it cannot be taken from you. When you purchase a game or movie online, you only purchase a licence to access it until the provider chooses not to provide it any more.
On a larger scale, documenting our cultural history in this situation necessitates piracy.
Army Attack Reborn
I used to play a game called Army Attack when I was 13, which was discontinued. Its holding company Digital Chocolate eventually went bankrupt, and most of its assets (including the copyright to this game) were acquired by RockYou Games, which itself went bankrupt later. Its assets were auctioned off, and the game assets are functionally untraceable. Media under similar circumstances are said to have been "orphaned", with "abandonware" being the term for abandoned software.
Army Attack Reborn is a fan-driven effort to recreate the game, and a major asset is the APK that someone extracted back when the game was active. Piracy for the win!
Emulators
Under similar justifications, emulators for discontinued gaming consoles can be justified. The Nintendo DS has been reverse-engineered to such an extent that fans are able to host replacements for DS Wireless Services too!
Of course, there exist emulators for active consoles as well. In fact, the USA does not even classify emulators as piracy. Nintendo has shut down two Switch emulators recently, the first of which was instantly forked.
While the first emulator, Yuzu, was taken down via a legal route, the second, Ryujinx, seems to have been killed via a backroom deal with the lead developer. The timing of this takedown is suspiciously close to reports of a Switch-exclusive game - The Legend of Zelda: Echoes of Wisdom - running better on the emulator than on the Switch itself.