Finite is a supply people can achieve over a certain time period. Like gold as an example, no fold miner or any other person can predict when all gold will be mine, even if estimated, it will be millions or billions of yeras, this makes gold infinite, unlike Bitcoin that almost 19 million are mined already. The total Bitcoin supply is 21 million in which over 98% would have been mined by 2050, this makes the supply finite. What some people argue is that the Bitcoin community can agree one day to increase the supply, but this can not happen because people would have even prefer if the supply is reduced which will help in Bitcoin price valuation also.