A more thorough explanation:

The symbiotic-relationship test is a standard used to determine if a private person can be considered a state actor and held liable for violating someone's constitutional rights. If the relationship between the private person and the government is so close that they can be said to be acting jointly, then the private person may be held liable for violating constitutional rights.

For example, in the case of Burton v. Wilmington Parking Auth., a restaurant in a public parking garage was held to have engaged in discriminatory state action by refusing to serve African-Americans. The Court found a symbiotic relationship between the restaurant and the municipal parking authority because the restaurant relied on the garage for its existence and significantly contributed to the authority's ability to maintain the garage.

However, the symbiotic-relationship test is strictly construed. The fact that an entity receives financial support from or is heavily regulated by the government is probably insufficient to show a symbiotic relationship. For example, in Jackson v. Metropolitan Edison Co., the Court refused to find a symbiotic relationship between a state and a public utility, even though the state had granted a partial monopoly to the utility.

In summary, the symbiotic-relationship test is used to determine if a private person can be held liable for violating someone's constitutional rights by showing a mutually dependent relationship between the private person and the government.