Measures of galaxy environment - I. What is 'environment'?

S.I. Muldrew, D.J. Croton, R.A Skibba, F.R. Pearce, H. Bae Ann, I.K. Baldry, S. Brough, Y-Y Choi, C.J. Conselic, Anna Rita Gallazzi, Stefano Zibetti