"Metroidvania" is a term used to describe a sort of exploratory 2D platforming game. It comes from the original games of the Metroid series and some of the middle-era of Castlevania games (most notably "Symphony of the Night", which is what primarily gave birth to the term).
The most defining feature is usually the world. Rather than have set stages or a world map, the entire game takes place inside one giant map, which you must traverse about. Not just any map, but typically a very complex map filled with all kinds of secrets. The map is typically divided into sectors, more in an aesthetic fashion to denote that the denizens and dangers will be different. Sometimes you have teleports to assist you in travel, but other times you just have to remember where to go in the map.
There's various elements at play in the exploration. There's typically tidbits hidden in spots, or puzzles that have to be returned to when you find appropriate equipment. The exploration is also non-linear - your limits of progression through the map are by various tools or powerups that you need to acquire, but the order in which you must acquire some of these tools is not set. And in many choices, there are many paths to get those tools, or even get past obstacles without those tools.
A very popular element of these games, especially in the Metroid franchise, is the concept of "sequence breaking". Using special tricks or otherwise mastering the utility of your basic abilities, you can sometimes access items and areas far earlier than the game expects you to.
As far as I know, Metroidvania games have always been 2D platforming games. Aside from the elements of exploration, the actual gameplay of Metroidvania games vary widely.
As InvaderSkoodge pointed out in his comment link to the origin of Rogue-likes
The roguelike genre takes its name from Rogue, a role-playing video game based on the Dungeons & Dragons role-playing games, including concepts such as stats and experience points.
Games that follow the Rogue trend will often include features such as:
- Randomized Dungeons
- Dungeons and Dragons based leveling
- Unforgiving difficulty (lack of a checkpoint system, perma-death, etc.)
Some good examples of rogue-likes, or games inspired by the roguelike genre, are FTL: Faster Than Light, Crawl, Brogue, Nethack, "Hack, Slash, Loot", and, obviously, Rogue.
Best Answer
Savescumming generally refers to the practice of reloading a saved game prior to a random event, repeatedly, until a favorable outcome is achieved.
The term originated in the Roguelike community, as the genre is known for the frequent occurrence of perma-death as a feature - in that community, any use of saved games to recover from a fatal mistake or poor roll of the dice, rather than restarting the game entirely, is considered to be unsporting or 'scummy' behavior.
These days, the term is often used in a variety of genres to refer to abuse of reloaded saves to yield optimal results.