It is the process of creating demand on a system or device and measuring its response.
In mechanical systems it refers to the testing of a system to certify it under the appropriate regulations (LOLER in the UK - Lifting Operations and Lifting Equipment Regulations). Load testing is usually carried out to a load 1.5x the SWL (Safe Working Load) periodic recertification is required.
In software engineering it is a blanket term that is used in many different ways across the professional software testing community.
Load testing generally refers to the practice of modeling the expected usage of a software program by simulating multiple users accessing the program's services concurrently.
As such, this testing is most relevant for multi-user systems, often one built using a client/server model, such as web servers. However, other types of software systems can be load-tested also.
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