Define law of demand and its assumption?

The law of demand states that, all else being equal, as the price of a good or service decreases, the quantity demanded by consumers increases, and vice versa. This inverse relationship is primarily driven by the substitution effect (consumers opting for cheaper alternatives) and the income effect (increased purchasing power as prices fall). Key assumptions of the law of demand include that consumers are rational, preferences remain constant, and there are no changes in factors like income or prices of related goods. Additionally, it assumes that the good in question is not a Giffen good, where higher prices may lead to an increase in demand.