If a currency is subject to inflation, that means the purchasing power of it will decrease over time. Meaning that the unit of that currency can not be used to buy as much as it used to.
Inflation can hurt if you are receiving a low salary. In a volatile inflation, it makes it hard for one to manage the budget effectively.
Many cryptocurrencies have fixed issuance rate. Bitcoin protocol for example has a fixed number of Bitcoin tokens to be issued which is 21 Million. That means, after that, nobody may mint more Bitcoin.
Source: Investopedia
Inflationary Cryptos
Some cryptos are inflationary meaning that the number of coins in circulation rises over time. Issuing new cryptos to network actors encourage participation.
Inflationary aren't only the ones having unlimited supply. It can also consist of the cryptos having limited supply. Some inflationary cryptos have fixed supplies while other have unlimited supplies meaning that there is no limit to token circulation.
Dogecoin, for example has unlimited supply. That means it could outpace the increases in demand for the crypto which could potentially decrease value of each Dogecoin over time.
Deflationary Cryptos
Supply of some of cryptos deflate over time which means as long as the demand for the crypto remains consistent the price for the individual crypto will rise.
Binance coin (BNB) for example is a deflationary currency. BNB crypto is burned/destroyed each quarter to reduce its supply after its supply touches 100 million.
Note: This is for information purpose. It's not a financial advice.