"A decree is a formal and authoritative order with the force of law, a judicial decision by order, a doctrinal act of a Church Council.
A decree is a law made by an authority or a Court decision."
"Legislation is the act or process of making and establishing laws."
(dictionary.com)
It varies from country to country.
For instance, Italian legislation focuses on immigration, equality, social rights and integration, 2023.

"In the UK Orders in Council are either primary legislation deriving their authority from the Royal Prerogative, promulgated by the Privy Council in the name of the Monarch, or secondary legislation promulgated by the minister of the Crown, using the authority granted by an Act of Parliament or other primary legislation." (Wikipedia) https://en.wikipedia.org/wiki/Decree
"A Constitution is the aggregate of fundamental principles or established precedents that constitute the basis of a polity, organization or other type of entity, and commonly determine how that entity is to be governed. Those principles written in one single document become a written Constitution.
The Constitution of the UK is notably a non-codified constitution, written in numerous fundamental Acts of legislature, court cases or treaties." (Wikipedia)
https://en.wikipedia.org/wiki/Constitution

If the Executive representative wants to implant a degree, these is known as "decreto-ley", only for penalty, tributary, elections or political parties he needs the aprobation of the President, Chief of Cabinet and the Ministers.
However the Constitution is above all the laws and there appears the Congress as representation of the people.