You've flummoxed me with this. The internet seems sure that "octameter" is a "metrical foot", which in this context is quite a pun. Without a link to confirm an architectural connection, I'll take this as a fairly obscure joke...
Haha, no, it's not a joke as I can tell you as an architect.
Sadly there are no english links, but have a look at Wikipedia [0] and you will see, that I've not dreamed that up :)
Of course it has a referenece norm: the DIN 4172, which calls it the "oktametrisches Maßsystem" (_octametric system of measurement_). It is made since a brick would be 11.5 cm and the mortice 1 cm = ∑ 12.5 cm. Eight bricks with mortice are a meter. Pretty easy actually!