Invitation to bid is an act of market transaction and finding business objects. Bidding refers to publicizing the conditions and requirements of goods, projects or services and procurement within a certain scope, inviting many bidders to participate in bidding, and then selecting the appropriate one as the transaction object according to the original prescribed procedures. Bidding is a trading method used in the sale of bulk goods, the contracting of engineering construction projects and the procurement and provision of service projects under the market economy. In this trading mode, the purchaser of project procurement (including goods procurement, project contracting and service procurement) is usually the tenderer, and the information of bidding procurement is released by issuing a tender announcement or issuing a tender invitation letter to a certain number of specific suppliers and contractors, and the nature of the required procurement project and its quantity, quality, technical requirements, delivery date, completion date or service provision time are put forward. And the qualification requirements of other suppliers and contractors, indicating that the suppliers and contractors that can best meet the procurement requirements will be selected to sign procurement contracts with them, and all interested parties will provide quotations for goods, projects or services needed for procurement and other conditions that respond to the bidding requirements to participate in the bidding competition. After reviewing and comparing the quotations and other conditions of all bidders, the tenderer selects the winning bidder and signs a purchase contract with it.