Technically, if you are employed, you have a contract, but the default terms of that contract in an at-will jurisdiction (e.g., every US state and D.C., at least) include the option for either side to terminate at will, hence the name.

Since the contract is terminable at will, reliance on it continuing into the future is generally unreasonable, and costs incurred based on such reliance will not generally be recoverable in the event it is terminated sooner than you expected.

Sorry, it is uncommon to have contract in US for Jobs? Or is this Tech specific ?

Edit: I had to look it up. US is indeed very business friendly..... May be a little too friendly.

I'm confused, what do get instead in the US when you're employed? I didn't know that contracts are not universal, over here I've never heard of anyone not having a contract.

At will employment still generally has a contract.