Bitcoin wallets based on connectivity
Wallets in which bitcoins are stored online and which are connected 24/7 to the internet are called hot wallets. Such Bitcoin platforms and services which can receive/withdraw bitcoins for their users are hot wallets. They are very much like the wallet you have in your pocket.
Akin to a cashier in a bank who has not kept the money deposited in the bank vault but left it on his/her desk, your bitcoins are always under threat when placed online and connected 24/7.
And you must have guessed, those bitcoins stored offline in hard drives or USB drives or paper, away from internet connectivity are called cold wallets.