A Soulslike (also spelled Souls-like) is a subgenre of action role-playing games known for high levels of difficulty and emphasis on environmental storytelling, typically in a dark fantasy setting. It had its origin in Demon’s Souls and the Dark Souls series by FromSoftware, the themes and mechanics of which directly inspired several other games.

From Wikipedia.

On top of what the other poster said, souls like means a very hard game that is insanely difficult. You might bang your head against a boss 85 times in a row and scream. Then after a break, you will 1 shot the boss.