The domain is just all the possible values that x can have for a specific function or relation.
For instance
$$y=\frac{7x^2-3}{x-4}$$
you cant divide by 0 so
$$\\x-4\ne 0\\
x\ne 4$$
but x can have any other value so the domain is
x is in the set of reals where x is not equal to 4
$$x\in R $ where $ x\ne 0$$
The domain is just all the possible values that x can have for a specific function or relation.
For instance
$$y=\frac{7x^2-3}{x-4}$$
you cant divide by 0 so
$$\\x-4\ne 0\\
x\ne 4$$
but x can have any other value so the domain is
x is in the set of reals where x is not equal to 4
$$x\in R $ where $ x\ne 0$$