What would you like to understand?

The likelihood function is a function of the unknown parameter $\theta$ after the observed data $x_1, \dots, x_n$ are fixed. It assigns to each candidate parameter value a measure of how likely the observed data are under that parameter.

Conditions: The data $x_1, \dots, x_n$ are treated as fixed observed constants.; The argument being varied is the parameter $\theta$.

The likelihood function is a function of the unknown parameter $\theta$ after the observed data $x_1, \dots, x_n$ are fixed. It assigns to each candidate parameter value a measure of how likely the observed data are under that parameter.

Conditions: The data $x_1, \dots, x_n$ are treated as fixed observed constants.; The argument being varied is the parameter $\theta$.