Literally, "the law of the place of the wrongdoing"
The full term is lex loci delicti commissi.
This concept comes up when discussing a tort or crime that takes place in multiple legal jurisdictions. In such a scenario, a court will have to decide which jurisdiction's laws apply. Lex loci delicti refers to the laws that apply in the place where the crime, copyright infringment for our purposes, was actually committed, rather than where the rightsholder lives, or where the right to the work were first received, etc.