A belief is an idea or principle which we judge to be true. Lives are routinely sacrificed based simply on what people believe. Our brains are attachment machines, attaching not just to people and places, but to ideas. And not just in a coldly rational manner.
Our brains become intimately emotionally entangled with ideas we come to believe are true, and emotionally allergic to ideas we believe to be false. This emotional dimension to our rational judgment explains a gamut of measurable biases that show just how unlike computers our minds are.
Philosophers typically divide knowledge into three types: personal knowledge, procedural knowledge, and propositional knowledge. The primary concern of epistemology is propositional knowledge, but contrasting this with other types of knowledge can help in clarifying precisely what it is that epistemologists are discussing.
The tripartite theory analyses knowledge as justified true belief, is widely used as a working model, even though most philosophers recognize that it has serious difficulties.
The closest thing to a rival to the tripartite theory is infallibilism, which suggests that knowledge requires absolute certainty, as opposed to belief or opinion about which there is more doubt.
The two concepts do overlap, but there's something about belief which distinguishes it from knowledge. I think that there are elements of belief where it overlaps with emotion and imagination, as opposed to rationalism and realism, which are the focus of knowledge.