The imposition of external constraints upon the behaviour of an individual or an organization to force a change from preferred or spontaneous behaviour. 
WHO Definitions of Regulations
WHO Health Systems Strengthening Glossary 
Regulation: the imposition of external constraints upon the behaviour of an individual or an organization to force a change from preferred or spontaneous behaviour. 
WHO Legislation and Regulation Website
"Laws and regulations are normally regarded as consequences of policy-making, but their implementation, or lack thereof, might lead to a process of further policy development. New laws and regulations may also be needed to address emerging environment and health problems."
Other Definitions of Regulations
Regulation is broadly defined as imposition of rules by government, backed by the use of penalties that are intended specifically to modify the economic behaviour of individuals and firms in the private sector. Various regulatory instruments or targets exist. Prices, output, rate of return (in the form of profits, margins or commissions), disclosure of information, standards and ownership ceilings are among those frequently used.
Context: Different rationales for economic regulation have been put forward. One is to curb potential market power and increase efficiency or avoid duplication of facilities in cases of natural monopoly. Another is to protect consumers and maintain quality and other standards including ethical standards in the case of professional services provided by doctors, lawyers, etc. Regulations may also be enacted to prevent excessive competition and protect suppliers from unstable output and low price conditions, to promote employment and more equitable distribution of income.
Excessive competition, sometimes also called ruinous competition, is a controversial term without precise meaning in economics. It usually refers to a condition of excess capacity and/or declining demand in an industry, which causes prices to fall to the level of average variable costs, discouraging new investment and causing some incumbents to leave the industry until capacity is reduced to the point where supply once again intersects with demand at a price sufficient to cover all costs. When regulatory authorities interfere with this process by setting minimum price levels, excess capacity and its attendant resource misallocation will tend to persist in the industry. Many economists use this as an example of the use of regulation to promote the private interests of producers at the expense of the public interest.
Not all forms of regulation have to be mandated or imposed by government. Many professions adopt self-regulation, i.e., develop and self-enforce rules commonly arrived at for the mutual benefit of members. Self-regulation may be adopted in order to maintain professional reputation, education and ethical standards. They may also act as a vehicle to set prices, restrict entry and ban certain practices (e.g., advertising in order to restrict competition).
Deregulation refers to the relaxation or removal of regulatory constraints on firms or individuals. Deregulation has become increasingly equated with promoting competition and market-oriented approaches toward pricing, output, entry and other related economic decisions.
PubMed Medical Subjects Heading (MeSH)
Exercise of governmental authority to control conduct.
Year introduced: 2003
Cases of Regulations
Center on Budget and Policy Priorities 
"On June 29, the Department of Health and Human Services (HHS) issued regulations regarding the Temporary Assistance for Needy Families (TANF) program. These regulations define the activities that are countable toward the work participation rate requirements, describe how the states must monitor and verify the hours that TANF recipients participate, and add some categories of parents who only receive benefits on behalf of their children to the work participation rate calculation.”
Hackey (1998) 
Three regulatory 'regimes' (based on US state health policy since 1960s):
"The author first concisely summarizes the evolution of state health care policies from the mid-1960s, including the substantial state variations in approaches to contain costs. The typology used in his model entails three categories of state "regimes" based upon the relationship between state government and the health care industry: 1) imposed regimes, with extreme centralization of state regulatory powers; 2) market regimes, characterized by underdevelopment of state regulatory authority; and 3) negotiated regimes, in which there is collaborative problem solving among public and private actors." [6,7]
 WHO Health Systems Strengthening Glossary https://cdn.who.int/media/docs/default-source/documents/health-systems-strengthening-glossary.pdf
 Saltman RB. Regulating incentives: the past and future role of the state in health care systems. Social Science and Medicine 2002;54:1677‐1684
 Glossary of Industrial Organisation Economics and Competition Law, compiled by R. S. Khemani and D. M. Shapiro, commissioned by the Directorate for Financial, Fiscal and Enterprise Affairs, OECD, 1993 http://www.oecd.org/dataoecd/8/61/2376087.pdf
 Hacket RB. 1998. Rethinking Health Care Policy: The New Politics of State Regulation. Washington, D.C.: Georgetown University Press.
 Wickson F. Environmental protection goals, policy & publics in the European regulation of GMOs. Ecological economics. 2014 Dec 1;108:269-73.
 Newman J. Evidence-based policy or risk minimisation? The regulation of e-cigarettes in Australia. Evidence & Policy: A Journal of Research, Debate and Practice. 2019 May 1;15(2):313-28.