What is a "tool strain"? When a biologist is talking about a genetically engineered mouse strain which is a "tool strain", what does that mean? What is the exact definition of a tool strain? What is the difference between a tool strain and any other mouse strain? Also, how are tool strains connected to recombinase techniques? Does using a recombinase automatically create a tool strain? Or are the properties "tool strain" and "recombinase containing strain" independent from each other? If it is important, the context is mouse (and possibly other animal) strains used in cancer research. It would help if you could keep the explanation high-level. I only have high-school biology knowledge and I am trying to make sense of the requirements for a software application for use by biologists.

In extension to shigeta's answer, I could well imagine "tool strains" and "recombinase strains" to be equivalent in the sense that they mean strains of mice whose genome you can easily manipulate.

Cre recombinase is an enzyme which can recombine (effectively insert) genes from a plasmid (which you somehow delivered to the cell) into the cell's genome, if Lox-sites are present (Cre-Lox recombination). This is a very common method of integrating genes into eukaryotic model organisms (i.e. mice).

By tool/recombinase strains they could simply mean mice which express recombinase already, so that you can readily insert your genes into specific cells by delivering a plasmid with the genes on it, and then triggering Cre recombinase in the cells you want to modify in order to integrate the genes into those cells' genome.