There are both forms and even a hybrid form (part of the application accesses shared bank and part uses isolated). This can still vary whether they are different business customers or companies within the group. Each one with its advantages.
There is no specific technology. It can be applied virtually in any technology.
One of the forms of this technique is called multitenancy .
Particularly, in the vast majority of cases, I think having a database for each company is the best solution. It gives more flexibility to climb, to customize, it is easier to give more security, in short, has a lot of specific advantages that is not the case. It gives more work to update, has more costs. It can automate to a certain extent. It depends on the application, depends on the need for data consolidation and a host of other technical and political factors. It gives extra work to keep everything as one.
In some cases you do not need to have separate banks, but schemas .
If you have specific questions applying the technique, please post it.