Explained in my words
What is Fungible/Non-Fungible?
Let's understand the definition of Fungible in a nutshell first. You have a 1 Rupee coin which is currently accepted everywhere (not vintage/rare) and you go swap that coin with one that your friend has. Still, you both got 1 Rupee in balance. Such kind of asset is called Fungible Assets, which can be swapped/replaced with the same type of asset and has equal value. On the contrary, let's say the coin you had was a rare vintage coin. Since the coin is not available much in the market and has more value due to various factors (attributes) it has a different value. Now, since the market value of the coin is different, you can't just go & replace it with 1 Rupee coin that your friend has. Such assets are called as Non-Fungible which cannot be replaced. Even if you take the same coin from the same year being rare, both of the coins will have different values based on the attributes like their mint condition, marks, etc.
We, humans, have used both kinds of assets right from the day we understood trading (barter trading days). When the internet came into the picture, we figured out a way of identifying a person using his/her username or password. However, we were never able to prove ownership and rarity of something on the internet using a centralized database technology that can be hacked or changed by mistake overnight. Imagine Mona Lisa painting's owner changed by an unknown hacker overnight since this was controlled by a website. No one would want to use such a system, hence we still used Government Bonds and Other documents for proving such things in addition to the databases which are just used for bookkeeping. Databases can still be wrong.
Then came the concept of Blockchain and Blockchain Contracts, Blockchain is a decentralized network of computers, which store information in such a cryptographic chain that a piece of Algorithm can never hack it. Believe it or not, Banks already use such kinds of setups along with the standard databases in form of Cloud and Distributed Computing to ensure the money of the Bank Customers remains intact. However, Blockchain contracts played a vital role in the birth of NFTs. Blockchain contracts to simplify can be explained as digital proof of a transaction stored in Blockchain publicly. People can view them but no one can manipulate them except the people (blockchain address) associated with that contracts, that too based on the permission given to those people.
NFTs are basically a digital proof of ownership to anything that can be digital: A meme, A video, A poem, A story, A film, An artwork, Manufacturing Design, Game Assets, Tickets to Events, Membership, Ticket to buy Physical things, which make use of Blockchain Contracts as proof if its rarity, uniqueness, value, and ownership. Just like the rare 1 Rupee coin that you had, NFTs which are usually traded get valued on their attributes. You might find two NFTs same by a picture, but their Attributes and hence their value differs. For example, an NFT ticket to a concert might look the same but based on their attributes, you get different swags and service offerings.
The big picture
The current landscape of NFTs is a little weird right now which makes this hard to accept for many people even me at a point looking at the sales of an Ape Picture, Cat Picture, etc. Almost 90% of these projects in a long run would fail if they don't prove and return its intrinsic value to their buyers. Even I tried minting dancing cats, which hardly a few people saw on Opensea. Here is a thing even if someone buys my cat as a collectible, what would they do with those cats, what do they get from it? Things started changing rapidly when Gary Vaynerchuk realized this thing's importance and showed them all how a project/NFT should be in the market. You should definitely learn about VeeFriends if you are reviewing NFTs. The token should hold a real value like the rare 1 rupee coin in the market, or it should at least add as a utility to an individual or an organization that is investing/buying. Moreover, I don't see NFTs just as an asset/product that should be used only for selling, I see it as a clear answer to the main problem of proof of ownership in the internet world. Here are some ideas I think would make more sense to have NFTs as:
NFT tokens to premium investors, won't be surprised if Kickstarter-like setups implement it.
NFT tokens to members of a business, group, community.
NFT tokens for connecting with your favourite people. This is something Big B (Bollywood Actor—Amitabh Bachchan), already understood and realized its importance.
NFT tokens for digital proof of financial transactions like the purchase of a home, etc.
NFT tokens for distribution of digital works like art, animation, film, songs, music, gaming assets if used with other blockchain contracts can help the art people earn more than they usually do traditionally.
NFT tokens for government administrations purposes. This can further become part of the cultural history and heritage of any nation once these NFTs go out of duty and become rare.
NFT for promoting international tourism.
The scam part
With great powers comes great responsibilities. People who are making this as a money hype these days don't really understand what this quote had to say. First, why I support NFT is not just because people are making $$ out of it, most will tell you it is a Crypto coin asset. What would you say if people start selling it in your own Fiat Currency Or issuing them for free as proof of transaction? Will it still be a crypto coin asset? NFTs are based on blockchain and hence the people who promote cryptocurrency started pushing cryptocurrencies with NFT. Personally, any currency which has no control of anyone can get shut down in minutes and no one would know whom to blame. It can lead to uncontrolled harm to humanity. I call NFTs to be highly inspired by a KNIFE. A product that everyone needs to use daily, but at times in the wrong hands can become fatal to innocents. It's important for everyone to stop avoiding NFTs and see how they can accept and implement this as an enabler.
The underlying Blockchain technology is known for its bad use of electricity. Hey, even the traditional banking systems drink a lot of electricity. Going forward, when I see a new Blockchain implementation, I see people already working towards making this technology Sustainable as it solves a specific problem. If someone brings something better than Blockchain, even that will be appreciated.