Assuming day 1 my wealth is 1. At day 2 I earned 20%. So the rate of return is 0.2 and the wealth at day 2 is 1.2. At day 3 I earned 50 % again. So the wealth at day 3 is 1.8. I wonder what is the value of 1, 1.2, 1.5 for each is called in academic?
It's called 'Gross return' (a.k.a. 'Gross Rate of Return'). See Zivot Course Notes Eqn. 1.8
Also, as pointed by Alex C:
... in Statistics it is called a 'link relative' or 'chain relative' (because it links together (via multiplication) adjacent terms of the CPI index or other time series)