Are MOUs legally binding?

I'm curious to know, are Memorandums of Understanding (MOUs) legally binding documents? I've heard they're often used in business negotiations and partnerships, but I'm not entirely clear on their legal status. Could you explain the nature of an MOU and whether or not it carries any legal weight? Additionally, if an MOU is not legally binding, what alternative options might be available for parties seeking to formalize their agreement in a legally enforceable manner?