Difference between RFI, RFP, RFT and RFQ in tender process

What is the definition and difference between:

RFI - Request for information
RFP - Request for proposal
RFT - Request for tender
RFQ - Request for quotation

The differences between each of the requests are quite essential. Purchasers use them in tendering process to select the best vendor. In some cases, to choose a contractor, only one of them is being used. It may also depends on the situation on the market.

RFI - Request for information is used for gaining information, preparation for an RFP or RFQ, forming a strategy or building a database with a purpose to identify potential vendors. It is often used when there are many potential suppliers. Procurement may use RFI to include a list of products for pricing requests. Sometimes it is used mainly for the registration of interest.

RFP - Request for proposal is a formal method of receiving detailed and comparable proposals from potential suppliers. It provides to procurement required information, that is needed to make an informed purchasing decision. RFP usually follows a RFI. Purchasers using RFP are often seeking solution based offers to meet their needs. In comparation to RFT, it is characteristic with greater flexibility.

RFT - Request for tender is a formal invitation to potential suppliers to bid to supply clearly defined products. It is focused on price and also on quality.

RFQ - Request for quotation is used when inviting potential suppliers to submit a bid on specific products or projects. The request is targeted primarily on pricing.

RFI is often the first step in the procurement process. It is used to find potential vendors and gather information about their capabilities. RFI is usually non-binding, meaning that is does not lead to a commitment to purchase.

RFP is a comprehensive process to get detailed proposals from potential suppliers. It usually goes beyond pricing and includes also other related aspects as quality, technical specifications, methodologies, timelines etc. Depending on governing law and jurisdiction, RFP is legally binding.

RFT is a formal invitation to potential suppliers to submit bids for a project. The process is highly structured and usually requires highly detailed project specifications.

RFQ is a formal request to potential suppliers to submit price quotations for specific goods or services. It is often primarily focused on pricing or quantifiable details.

What does it mean that "RFP is legally binding" ?
How does it impact the tender process ?

RFP is a request for proposal. It is a procurement process, but also a business document.

RFP is used to ask potential suppliers to submit their proposals for a delivery of specific project, good or service. Submitted RFP documentation is often not strictly a contract document, but it is used as a basis for contract negotiations.

In some cases, RFP documentation can be considered as a contract itself, if it contains all the necessary details.

So information you provide in RFP documentation are legally binding. For example, if you provide a pricelist within a RFP, you should deliver goods or services at prices included in this pricelist.