After doing some research into the topic, the question as to what a game is would be more complicated than you may think.
At face value, a game can be pretty much anything as long as its interactive and brings entertainment to the player. But then the problem lies, what isn't a game? Thing is, it's not as simple as if you can win or lose at it, it's a game. It's much more than that. There are the classic multiplayer games like FPS or one on one games with a solid goal of one side winning over the other, a solid example being red vs blue, but when you look at the entire industry, there's more to be accomplished. Some games are more focused on storytelling while some others may have multiple interpretations and players play differently based off of their interest. The iconic game Minecraft is a good example. Some may find interest in the single-player mode where you beat the so called ender dragon while some others may find interest in designing nicely built houses or other monuments, playing online in public multiplayer servers where the game list could from PvP to sharing your builds with others and so much more. What am I trying to get at here? Games can be very subjective, but as a whole, I'd like to describe a "game" as something with an goal in mind to accomplish something. Decisions take a big part in this but as a whole, interaction is key. As long as the player can physically do something and take something out of it (a moral lesson, idea, skills, etc. that the developer may or may not have had in mind while making said game), be hopefully entertaining, have a goal in mind... it's a game.
At first, I had difficulty with understanding what was a game and not a game considering visual novels were on the fuzzy line between game and not game. I did some digging and it turned out that yes, it was a game. It depends because though it's linear and does a lot of reading, the player can make decisions and in some specific VNs there are puzzle games to make it more interesting, etc. One has to interact with the game, if not, you couldn't go any further, it wouldn't run on its own. There are different endings, decision making, etc. that make it, well... a game. Down to its very core, a game is an "interactive experience," as ChrisDeCoster would put it. From another point of view, I'd like to add that a game could simply be one where you and a friend try and guess songs from each other's playlist. It doesn't have to be majorly complicated to be one.
Someone online with the user SangoProductions213 made a good comment saying that a good definition of a game is; "Playing a game is the voluntary attempt to overcome unnecessary obstacles." It would include four defining traits being a goal, rules, a feedback system, and voluntary participation.
Lastly, and most personally, I'd like to go over briefly what the sides are in the argument usually. On one side are the abstractionists who believe in pushing the boundaries of what a game is, somewhat similar to narratology whereas they believe the "game's value depends on its narrative." The other side of the coin would be the game formalists that believe a game should meet some specific requirements, challenge, competition, etc. to be called a game, similar to ludology which is a "perspective that a game's world and rules are what make the game valuable." Personally, I'd fit into the abstractionist category. I believe that almost anything can be a game if there's a goal in mind and if people can take something great out of it, whatever it may be.
Some references:
> What is a game? And why it matters! | Game/Show | PBS Digital Studios
> Are Visual Novels Video Games? Well, It Depends…
> Can visual novels be classified as a videogame?
(If you couldn't tell, VNs helped me distinguish a lot between a game and non-game.)
NOTE: Honestly, I had a very hard time trying to comprehend whether something's a game or not. Who's not to say something can be a game? As long as someone finds entertainment and some kind of goal, etc. a lot of things can be a game. Even playing with someone's mind like psychology tricks or something similar could count as playing games with people and their minds. Does it really have to be defined so deeply? I want people to just have fun. In the end, though, I did my best to professionally describe what it means to me. I did my research and it's a challenging question that many disagree on, I guess I could say this is just my opinion.