"Purchase rules" refers to the set of rules and regulations governing the acquisition of goods and services, which can vary significantly depending on the entity making the purchase (e.g., public sector, private business). Common principles for public purchases include making them in the most economical manner, avoiding splits to bypass authority, and purchasing based on definite needs, while private sector purchases are often guided by terms and conditions in purchase orders. Key components often include financial delegation, requirements for quotations or competitive bidding, and guidelines on contract execution and supplier reliability.