In electrics what does PAT mean?

PAT Testing stands for Portable Appliance Testing.

The correct full name is 'In-service Inspection & Testing of Electrical Equipment'.

'PAT Testing' term is known as a tautology (unnecessary or unessential (and sometimes unintentional) repetition of meaning).*

Another example on wikipedia for this is 'short summary'; a 'summary' is a 'shortened' version of a text.

It is perfectly common to write PAT Testing, PAT Tester and PAT test. In the industry they are known as 'PAT Testers' to do 'PAT Testing' to carry out a 'PAT Test'.

This answer is spot on, to add to it, the method of PAT testing is the practice of electrical and safety testing on electrical appliances, to ensure an appliance is safe and thus won't give someone a shock.