A multiple linear regression model is used to predict the value of a single dependent variable based on the values of two or more independent variables.

A multiple linear regression model is used to predict the value of a single dependent variable based on the values of two or more independent variables.

• a. A model with two or more independent variables predicting one dependent variable. This accurately describes multiple linear regression, where "multiple" refers to the independent variables.
• b. A model that explains the relationship between two dependent variables. This is incorrect; regression models typically have one dependent variable.
• c. A model where all variables are dependent. This is incorrect; regression models distinguish between independent and dependent variables.
• d. A model with one independent variable predicting one dependent variable. This describes simple linear regression, not multiple linear regression.

Therefore, option a is the best description.

$\boxed{a. A model with two or more independent variables predicting one dependent variable}$