this is a fictitious or bogus transaction

if it wasn't terminus technicus, one could even say "phoney/phony", a little stronger of a word though

See section 340 (1)-(5) HGB [http://dejure.org/gesetze/HGB/340b.html] for the definitions. Strictly speaking, one would have to qualify the fact that the repo lender has the right, but not the obligation, to return the underlying securities. In practice, however, this distinction is not expressly made (not least because this concept does not exist in a similar way in English law, for instance) If you would like to distinguish between the two in your English text, one possibility is to refer to "echte Pensionsgeschäfte" as "repo/reverse repo transactions" (adding the German term in brackets in each case, at least when using the term for the first time).

Note that "reverse" only denotes one particular side to the transaction.