A hot wallet is one that is online, quick and easy to use for bitcoin trading or spending, but it is also vulnerable to cyberattacks, which can result in lost or stolen bitcoins, for example. Edge wallet, coinbase, and Metamask
The reason you can just get a hardware wallet instead if you are the type that makes frequent transactions. For online wallet, I will prefer Electrum which is open source and not a web or web extension wallet.
A cold wallet is one that is not connected to the internet, such as paper, USB, and other computer storage facilities where the private key can be kept, such as CDs.
But know that the ones that are generated on perfectly airgapped device should be regarded as cold wallets.