Is Random function (in any programming language) biased?

Is the function Random in programming languages not biased? After all, the algorithms need to be based on something, and that can generate bias. According to this website https://mathbits.com/MathBits/CompSci/LibraryFunc/rand.htm, rand() function needs a start number, called seed. It states that

the rand( ) function generates a pseudo-random sequence

I don't completely understand the logic behind it. If it's not really random (pseudo-random), is there a way to make it perfectly random?