What is the difference between back and backing welds?

Back welds and backing welds serve different purposes in welding. A back weld is a weld applied to the reverse side of a joint, typically to reinforce it or ensure complete fusion, while a backing weld is a type of weld made on a backing bar or plate that supports the root of the weld joint, helping to prevent defects and provide a solid foundation. Essentially, back welds reinforce the joint, whereas backing welds provide support during the welding process.