A Contact is an individual or company that the practice may come in touch with. They may be a suppliers of products or services to the business — For example, banks, solicitors or tax agents — or prospective clients that the practice may want to keep in the database. The details might be their name, addresses, phone numbers, email addresses, et cetera. The amount of information you keep on a contact is up to the practice.
Once you attach assignments and charge them for work done, a contact is considered a client.