"Jerry" was a slang term for a German person during World War II.
Miles O'Brien and Julian Bashir (as well as Quark) used the term when O'Brien and Bashir used their Battle of Britain holoprogram. (DS9: "Homefront", "Accession", "Looking for par'Mach in All the Wrong Places")
Quotes
"All right, all right. I'd hate to let the "Jerries" strafe that "green and pleasant land" of yours while you two were taking time outfor a drink." - Quark
"So, want to go back up and take another crack at the Jerries?" - Bashir
"And let the Jerries get across the channel, never." - O'Brien
"You know, I heard a rumor that the Jerries might be coming over the Channel tonight. Should we have a little surprise waiting for them?" - Bashir