1- ARCH- Autoregressive Conditional Heteroscedasticity-

The AR comes from the fact that these models are autoregressive models in squared returns, The conditional comes from the fact that in these models, next period’s volatility is conditional on information this period. In an ARCH(1) model, next period's variance only depends on last period's squared residual so a crisis that caused a large residual would not have the sort of persistence that we observe after actual crises.