They are not a contract by themselves but they can absolutely be used to specify the details of the main contract the customer is about to enter, for example by buying something in an online shop, etc. and that contract is then in its entirety binding (assuming no laws are broken etc).
As far as I know it’s not legally binding pretty much anywhere. They’re not legal contracts because they don’t fulfill the requirements of one.
They are not a contract by themselves but they can absolutely be used to specify the details of the main contract the customer is about to enter, for example by buying something in an online shop, etc. and that contract is then in its entirety binding (assuming no laws are broken etc).