They're interchangeable depending on what literature you read. Funnily enough, like ATM machine, DIP package can be redundant, being equivalent to "dual in-line package package".

I think I just picked this up from my father, who’s an old-school hardware hacker. So it’s either oldfashioned lingo (he’s been retired 20 years or so) or British or both :) Or perhaps I’m just confused, given I’m mainly a software guy.

i'm gonna guess it's because L and P are next to each other on the keyboard.