What is State Ownership?

Legal Definition
State ownership (also called public ownership and government ownership) refers to property interests that are vested in the state or a public body representing a community as opposed to an individual or private party. State ownership may refer to ownership and control of any asset, industry, or enterprise at any level (national, regional, local or municipal); or to non-governmental public ownership. The process of bringing an asset into state ownership is called nationalization or municipalization. State ownership is one of the three major forms of property ownership, differentiated from private, cooperative and common ownership.

In market-based economies, state-owned assets are frequently managed and operated as joint-stock corporations with a government owning either all or a controlling stake of the shares. This form is often referred to as a state-owned enterprise. A state-owned enterprise might variously operate as a not-for-profit corporation, as it may not be required to generate a profit; as a commercial enterprise in competitive sectors; or as a natural monopoly. Governments may also use the profitable entities they own to support the general budget. The creation of a state-owned enterprise from other forms of public property is called corporatization.

In Soviet-type economies, state property was the dominant form of industry as property. The state held a monopoly on land and natural resources, and enterprises operated under the legal framework of a nominally planned economy, operating according to different criteria than state and private enterprises in capitalistic market and mixed economies.
-- Wikipedia
Legal Definition
The governement owns at least 51% or controlling share of the company. It is known as nationalisation when it is completely owned by the general public.