The name derives from two words, one in Italian “Osteria” and one in English “Running”.
I used to do a lot of running and a friend of mine used to ask me at lunch time each day
but my other hobby is eating well and being in Italy there are lots of Osterie (restaurants). On this particular day to express that I wouldn’t be running I replied
No, today I’m Ostering.
and so was born a new word.