As I understand it (the system has recently changed), 'Ltd' indicates a privately owned company while 'PLC' indicates a public limited company whose shares can be bought at the stock exchange. In both cases, by legislation and upon registration, the company becomes a financially responsible entity distinct from its owner(s), so that company liabilities are not the personal liabilities of the owner(s). This means that if the company goes bankrupt, for instance, its payback of outstanding debt is limited to what the company's liquidated assets can reimburse.
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