Analysis of Covariance (ANCOVA) includes one or more continuous explanatory variables to test whether there are differences between groups controlling for those continuous explanatory variables. For a continuous response $Y$, a two-level factor $Z$ and a continuous covariate $X$, the ANCOVA model can be specified as $Y_i = \beta_0 + \beta_1 Z_i + \beta_2 X_i + \epsilon_i$ In this case, the slope of the line for each factor will be the same (given by $\beta_2$) while the intercepts will differ ($\beta_0$ for the control and $\beta_0 + \beta_1$ for the second group).