Is it possible to unlock a verizon wireless locked iphone 5s?

What is the difference between a locked and an unlocked iphone? Can we use other sim cards in a locked one? Thank you.

No its not. The same speaks for itself. Verizon wireless phones do NOT have a slot for Sim cards. The rest is self explanatory. And no right now its not only difficult to unlock iPhone 5S but you might not be able to evade the contract and even if you do you will end up paying a huge amount for unlocking it which will all together cost more than an Factory unlocked iPhone 5S.

The Verizon iPhone 5s is sold unlocked already.

No you can't use other carrier SIM cards in a locked one.