Let's talk about supply.
The maximum supply of BTC is limited to 21 million only. It is deflationary by nature. It is estimated that up more or less 20 percent of its total supply is already lost and could not be retrieved anymore.
Other coins like ETH have a constant flow of new coins added to the ecosystem which makes it inflationary like fiat currencies. Although that could change next month as EIP-1559 introduces a fee-burning mechanism that will permanently remove coins from the total circulating supply.
If you are oftentimes looking at CoinGecko or Coinmarketcap, you might have noticed the terms 'circulating supply, 'max supply' and 'total supply.' Related to these terms are 'market cap' and 'fully diluted market cap.' Let me explain each term briefly and concisely and in an easy-to-understand way.
Some may not care about these terms but these are in fact necessary when doing your investment analysis. That also prevents you from buying high supply shitcoins which does not have any real use case and demand at all to make their growth truly sustainable.
Circulating supply is the number of assets that are circulating in the market and in the general public's hands. This also includes coins which are already deemed lost due to lost of private keys. For example, the circulating supply of Bitcoin is 18,760,218.00 BTC.
The circulating supply when multiplied to the price of the coin results to the market cap. For example, the market cap of Bitcoin at the time of this writing which is USD 592,220,090,085 is the product of its circulating supply of 18,760,218.00 BTC and price which is USD 31,567.96.
Total supply is the amount of coins that have been already created, minus any coins that have been burned. For example, let us say (just assuming since Bitcoin does not have a burn mechanism in its tokenomics) 1,000,000 BTC was burned, Bitcoin's total supply will be 17,760,218.00 BTC.
So let us go to the maximum supply. It refers to the maximum amount of coins that will ever exist in the lifetime of the cryptocurrency. As I mentioned above the maximum supply of Bitcoin is 21,000,000 BTC. For Ethereum that changes everytime since new ETH are being mined by miners.
The max supply when multiplied to the price of the coin results to the fully diluted market cap. For example, the market cap of Bitcoin at the time of this writing which is USD 663,898,105,459 is the product of its max supply of 21,000,000 BTC and price which is USD 31,567.96.
I hope this makes everything easy.