G2B (Government to Business) is a term that refers to the relationships between organizations (subjects) of public administration and enterprise (business). The designation can be used for any relationship between the subject of public administration and the enterprises as one of the basic e-goverment models (other model are G2E, G2C or G2G).

In G2B model the initiative comes from a government organization and 

In G2B model the initiative comes from a government organization and businesses are the target group.
Some sources distinguish also B2G (Business to Government) where the initiative comes from businesses, while other sources consider both G2B and B2G as equal without important no significant difference, ie. with the same meaning.

Example:

Business to business to consumer (B2B2C) is an e-commerce model that combines business to business (B2B) and business to consumer (B2C) for a complete product or service transaction. B2B2C is a collaboration process that, in theory, creates mutually beneficial service and product delivery channels. 

B2B2C is a business model where online, or e-commerce, businesses and portals reach new markets and customers by partnering with consumer-oriented product and service businesses. A business developing a product, service or solution partners with another business to use a particular service, such as an e-commerce website, portal or blog. The two business combine forces and promote mutually beneficial products, services and/or solutions.

Example :

1) Manufacturer + Distributor + B2B Customer

Another form of C2B is the electronic commerce business model in which consumers can offer products and services to companies, and the companies pay the consumers. This business model is a complete reversal of the traditional business model in which companies offer goods and services to consumers 

C2B is a kind of economic relationship that is qualified as an inverted business type. The advent of the C2B scheme is due to:

There are five common types of B2C online business models. Below is a brief description of them.

This is a very popular model. Companies offer a wide variety of goods and services to people online.

Intermediaries don’t offer anything of their own. Instead, they offer their platform to users so that they can buy or sell products.

Online communities offer an open space for companies to advertise their brand or products to platform users.

Advertising-based companies offer key advertising features to attract specifically end-consumers in large volumes.

Fee-based companies offer their services, products, or benefits to people in exchange for a fee.